ABSTRACT
Unconsolidated deposits-mainly
glacial driftoverlie bedrock and form the land surface i n most of Illinois.
These unconsolidated d e p o s i t s , which c o n s i s t of various
sediments transported by i c e , wind, and water, a r e parent
materials for most Illinois s o i l s , are important sources of
building products and ground water, and affect land u s e ,
mining, construction, and drilling operations.
As shown by t h e drift thickness map of t h e s t a t e
included in the report, glacial drift ranges from l e s s than
a few feet t o about 600 f e e t i n t h i c k n e s s . Throughout t h e
state, the t h i c k e s t drift occurs i n major v a l l e y s cut into
bedrock, and, regionally, it occurs i n t h e northeastern
quarter of t h e s t a t e , the part that w a s covered by t h e l a s t
(Wisconsinan) glacier. The thinnest drift-less
than 25
feet thick and intersected by numerous bedrock outcropsoccurs widely i n southern and western Illinois.
INTRODUCTION
Most of the landscape of Illinois i s developed on earth materials deposited by great continental glaciers of the geologically recent Ice Age, by wind,
and by streams These materials, generally unconsolidated, mantle the much
older, layered bedrock-mainly s h a l e , lime stone, and sand stone-that extends
downward t o t h e ancient crystalline basement rocks.
Most of the unconsolidated deposits are t h e result of glaciation and
commonly are called glacial drift or simply drift. The unconsolidated d e p o s i t s
.
h his
r e p o r t , i n c l u d i n g d r i f t t h i c k n e s s map and c r o s s - s e c t i o n s , r e v i s e s and updates
C i r c u l a r 416 (19671,which was prepared by t h e same a u t h o r s and i s now out of p r i n t .
1
I L L I N O I S STATE G E O L O G I C A L SURVEY C I R C U L A R 4 9 0
include unsorted, ice-laid rock d e b r i s , called t i l l ; sorted meltwater-laid sand
and gravel, called outwa sh; fine-grained sediments laid down i n glacial l a k e s ;
wind-blown s i l t , called l o e s s ; and fine- t o coarse-grained sediments of modern
streams. They range from 1 or 2 feet t o about 6 0 0 feet in t h i c k n e s s .
The t h i c k n e s s and character of the glacial d e p o s i t s a r e of interest for
several r e a s o n s . The most fertile s o i l s of Illinois a r e developed on the unconsolidated d e p o s i t s , and most buildings and roads a r e constructed on them.
They a r e important sources of building materials and ground water, and t h e y
must be penetrated or removed in a n y mining operations that go into the bedrock.
Purpose of Study
The purpose of t h i s study i s t o describe t h e t h i c k n e s s , distribution, and
character of the unconsolidated deposit s-e ssentially the drift-of Illinois. Emp h a s i s is on t h e physical c h a r a c t e r i s t i c s of t h e drift materials rather t h a n on
their a g e or stratigraphic relations. The basic data for the study of drift thickn e s s a r e primarily well records from the f i l e s of t h e Illinois State Geological
Survey t h a t have been systematically examined i n s t u d i e s of drift aquifers during
the p a s t 1 1 years. These records have been provided by drillers, consultants,
oil operators, industrial and municipal officials, and cooperating s t a t e and federal a g e n c i e s . Piskin and Bergstrom (1967) reported on t h e t h i c k n e s s and chara c t e r of t h e glacial drift i n Illinois in Circular 416, which i s now out of print.
This report r e v i s e s and updates Circular 416.
Presentations of the stratigraphy, a r e a l distribution, and character of
the drift a r e summarized from t h e work of other investigators, a s cited in the
t e x t . Additional d e t a i l s on the drift may be obtained from the published reports
referred t o here. The most important of t h e s e is Leland Horberg's report (1950)
on the bedrock topography of Illinois, i n which t h e bedrock surface map of t h e
s t a t e i s included. This map, reprinted by the Illinois State Geological Survey
on a s c a l e of 1:500,000 i n 1957, complements the drift t h i c k n e s s map (pl. 1) of
t h e present report. Another major source of information on the history, c l a s s i fication, distribution, and physical characteristics of the glacial d e p o s i t s is a
report on the Pleistocene stratigraphy of Illinois by Willman and Frye (1970), i n
which geographic names a r e assigned t o formations and members of the Pleistoc e n e Series, t o buried s o i l s , and t o d e p o s i t s a s s o c i a t e d with certain landforms
such a s glacial end moraines. Willman and Frye's report gives a classification
for t h e various Pleistocene units similar t o that i n u s e for the bedrock formations.
Such a classification will eventually provide a b a s i s for delineating t h e distribution and specific characteristics of t h e various materials described in general
terms i n the present report. The nature of the bedrock formations below t h e drift
and the general features of the drift a r e shown on t h e s t a t e geologic map published by t h e Illinois Geological Survey (Willman and others, 19 67)
It i s anticipated that the information presented in t h i s report h a s potential
application t o the study of both regions and s i t e s . This information bears on
ground-water exploration and development, drilling procedures, mining operat i o n s , construction, and waste d i s p o s a l , i n which t h e following a s p e c t s a r e
pertinent: (1) t h i c k n e s s of drift (areas of thick drift or overburden, of thin drift,
and of rock outcrop; depth t o bedrock); (2) distribution of drift (location of
outwash-filled bedrock v a l l e y s , moraines, lake plains, thick l o e s s , and drift
borders); and (3) nature of drift (texture of beds, vertical and lateral variability;
presence of aquifers, impermeable b e d s , weathered zones, and l o e s s )
.
.
T H I C K N E S S AND CHARACTER O F GLACIAL DRIFT
3
ORIGIN OF DRIFT
For convenience, the terms "drift" and "unconsolidated d e p o s i t s " a r e
used synonymously in t h i s report t o refer t o t h e g l a c i a l , interglacial, and Holocene
("Recent") d e p o s i t s of t h e Pleistocene Series (table 1), representing t h e l a t e s t
division of geologic time. (Technically, t h e term "drift" i s restricted t o t h e glac i a l till and interbedded s i l t , sand, and gravel i n t h e glaciated region and d o e s
not include the l o e s s that mantles t h e s e deposits nor t h e recent alluvium along
the stream valleys. Similarly, t h e term "unconsolidated d e p o s i t s " includes consolidated, or cemented, sand and gravel i n l o c a l a r e a s but d o e s not include unconsolidated older formations, such a s the Cretaceous and Tertiary d e p o s i t s of
southern and we stern Illinois .)
As suggested by table 1 , t h e Pleistocene history of Illinois, though
geologically brief, i s complex. Willman and Frye (19 7 0) detail t h i s history.
From t h e time of the Nebraskan glacier, which advanced into midwestern United
States from a n i c e center i n northern Canada about a million years ago, Illinois
h a s been repeatedly overridden by g l a c i e r s . The glaciers, carrying great quant i t i e s of rock debris, flowed southward during periods of cold and increased
precipitation and then melted a s t h e climate warmed. Drift s h e e t s left by the
glaciers were weathered during long, warm interglacial s t a g e s . For example,
the Illinoian glacier advanced southward t o Carbondale (fig. l ) , and during the
Sangamonian Stage (interglacial) t h a t followed, drift from the glacier w a s weathered a s deeply a s 15 feet (Horberg, 1953, p . 28).
Wisconsinan drift w a s deposited on t h e weathered Illinoian drift i n much
of Illinois. Later, Holocene deposits of diverse origins were distributed
over t h e glacial and interglacial s e q u e n c e s . Logs of representative wells passing
through t h e drift a r e given i n t h e appendix.
Types of Deposits
The relations of the various earth materials of t h e drift t o t h e land surf a c e , glacial features , and bedrock surface a r e diagrammatically illustrated i n
figure 2 . Glacial d e p o s i t s c a n be differentiated into t h o s e deposited directly
from t h e i c e (till) and t h o s e modified by the a s s o c i a t e d meltwater into glaciofluvial (glacial river) and glaciolacustrine (glacial lake) d e p o s i t s . Thornburn
(1963, p. 16-25) presents a pertinent d i s c u s s i o n of the character and origin of
the glacial and related d e p o s i t s of Illinois. Willman and Frye (1970) l i s t and
systematically describe t h e s e d e p o s i t s .
Till
Till i s ice-laid debris-a mixture of fragments of a l l sizes-rarely with
any stratification. Commonly, i t h a s a matrix of s i l t , c l a y , and sand i n which
pebbles, cobbles, and sometimes large boulders are imbedded. It occurs i n t h e
form of ridges called end moraines and intervening undulatory plains called
ground moraines or till plains. The names of moraines, s u c h a s "Cerro Gordo
Moraine, " refer t o the end moraines. Ground moraines, if named, bear t h e same
name a s the end moraine with which t h e y a r e a s s o c i a t e d , for example, "Cerro
Gordo ground moraine." "Cerro Gordo Drift" refers t o d e p o s i t s of both end and
TABLE 1 - CLASSIFICATION AND CHARACTER OF PLEISTOCENE DEPOSITS (DRIFT) I N ILLINOIS
(For more complete c l a s s i f i c a t i o n , s e e Willman a n d Frye, 1 9 7 0 , and Johnson et a l . , 1972)
YEARS BEFORE
STAGE
PRESENT^
SUBSTAGE
PRINCIPAL NAMED
DEPOSITS
KINDS OF DEPOSITS
C l a y s , s i l t s , s a n d s , and gravels of present
streams; slopewash sediments; lake and beach
sediments; dune sands; swamp peat and muck.
HOLOCENE
I
7,000X
VALDE RAN
TWOCREEKAN
Cahokia Alluvium
Outwash.
Weathering products; not prominent i n Illinois.
11,000*
12,500*
In
01
a,
S
WISCONSINAN
MORAINES AND
MORAINIC SYSTEMS
WOODFORDIAN
C
$g
m
-"
Tills, i n many well developed moraines; l o e s s ,
outwash; lake sediments.
2
p
P,
Lake Border M. S.
Many named moraines
Shelbyville M S.
.
22, OOO*
FARMDALIAN
ALTONIAN
28, 000*
1
.$ 3
Silt, muck, and peat.
I Thick, extensive l o e s s e s ; t i l l s ; outwash.
1
I
I
I
2
2
75,000
SANGAMONIAN
earn
Soil and weathering products; accretion-gley
(slopewash) d e p o s i t s .
I
;0
2.i
5
2
r7
-
Buffalo Hart
/Jacksonville
Oak Hill
William sfield
Oneida
Table Grove
Mendon
JUBILEEAN
Tills, some i n morainic forms; fossiliferous
s i l t s ; outwash; mixed ice-contact d e p o s i t s .
ILLINOI AN
MONICAN
LIMAN
YARMOUTHIAN
s
(slopewash) d e p o s i t s .
o
s
E
&
KANSAN
Till, outwash,and slackwater s i l t s .
L
Mahomet and
2
Soil and weathering products; accretion-gley
(slopewash) d e p o s i t s .
AFTONIAN
NEBRASKAN
Till and outwash of uncertain extent.
1,000,000
'~rorn radiocarbon dating* or estimation.
0
E '
2 !f
Sanko:y Sand
Members
\_
T H I C K N E S S AND CHARACTER O F GLACIAL DRIFT
ground moraines and a l l d e p o s i t s of the glacier that deposited t h e Cerro Gordo
Moraine. The named drifts a s s o c i a t e d with landforms such a s moraines a r e
units within a morphostratigraphic ( m o r p h =
~ form) cla s sification of Pleistocene
d e p o s i t s (Willman and Frye, 1970).
The end moraines record t i m e s when t h e i c e front temporarily maintained
a fixed position. The moraine w a s built a s rock debris w a s carried t o the melting
i c e front. The intervening plains between end moraines record times when t h e
front of t h e glacier melted back.
In composition, t h e t i l l s of Illinois range from d e n s e clayey s i l t with
few pebbles t o gravelly sand containing abundant stratified, water- sorted
material. The finer grained t i l l s a r e much more abundant than t h e coarser
grained.
Glaciofluvial Deposits
Glaciofluvial d e p o s i t s were laid down by meltwater t h a t was discharged
along the front of t h e i c e and through c r e v a s s e s , t u n n e l s , and channels extending back into the i c e . The meltwater contained rock debris ranging from c l a y
and rock flour t o gravel. In response t o changing volume and velocity of flow,
t h e meltwater sorted t h e particles a s i t deposited them downstream. Sand and
gravel generally were deposited a s outwash plains c l o s e t o t h e i c e front, a s
along the moraine shown i n figure 2, or a s valley trains i n channels t h a t led
meltwater away from the i c e . The finer particles were carried farther, often not
settling until t h e y reached the quiet water of a lake. Other glaciofluvial deposi t s were formed a s e s k e r s , fillings of meltwater channels that flowed on or below t h e i c e , or a s kames, mounds of sediment where meltwater cascaded into
holes i n the i c e .
The glaciofluvial d e p o s i t s , especially the valley trains t h a t are extensive along major valleys such a s t h o s e of the M i s s i s s i p p i , Illinois, Rock, Kaskaskia, and Green Rivers (fig. l ) , a r e important sources of sand and gravel and
constitute t h e most widely used aquifer system i n Illinois.
Glaciolacustrine Deposits
Glaciolacustrine d e p o s i t s c o n s i s t of well-sorted sand and gravel accumulated along beaches of glacial l a k e s by wave action; inclined sand and gravel
beds laid down i n d e l t a s ; and fine sediment t h a t settled i n quiet waters offshore.
Many glacial l a k e s formed behind end moraines i n t h e northern half of Illinois
and in sediment-dammed river valleys i n t h e southern half of Illinois (fig. 1 ) .
In t h e s e places lake sediments form a veneer over glacial till. Fraser and Steinmetz (1971), Willman, Leonard, and Frye (1971), and Frye e t a l . (1972) have
reported on t h e conditions of deposition, nature of d e p o s i t s , and t h e faunas i n
some of t h e Pleistocene l a k e s . Gross e t a l . (1970), Lineback, Ayer, and Gross
(1970), Lineback e t a l . (1971), Lineback, Gross, and Meyer (1972), and Lineback and Gross (1972) have reported on the Pleistocene d e p o s i t s on t h e floor of
Lake Michigan.
Wind-Blown Deposits
Wind -blown sediment, chiefly s i l t , was widely distributed i n Illinois
during t h e glacial s t a g e s . The source of much of t h e s i l t w a s t h e river valleys
that were partly filled with coarse - t o fine-grained glacial outwa s h (Leighton
and Willman, 1950, p 606). The river f l a t s , kept free of vegetation by frequent
.
6
I L L I N O I S STATE G E O L O G I C A L S U R V E Y C I R C U L A R 4 9 0
Fig. 1
- Glacial
1970).
geology of Illinois (modified from maps by Willman and Frye,
THICKNESS AND CHARACTER O F GLACIAL DRIFT
7
I L L I N O I S STATE G E O L O G I C A L SURVEY C I R C U L A R 4 9 0
glacial flooding, were subject t o wind erosion, and great volumes of silt were
blown onto the uplands bordering the valleys and formed l o e s s deposits. Because
the winds were generally from the northwest, the l o e s s deposits are thicker on
uplands e a s t of the main river valleys than on uplands west of the valleys (figs.
1 and 2 ) . In some places on t h e e a s t side of wide flats of the Mississippi and
Illinois River Valleys, from 50 t o almost 100 feet of l o e s s c a p s the river bluffs
(Smith, 1942). The l o e s s becomes finer grained and thins rapidly away from the
river valleys, but i s widespread in the s t a t e . Loess deposits occur interbedded
with glacial t i l l s and a s a mantle over some of t h e uppermost t i l l s .
Products of Weathering
The effects and products of t h e interglacial stages are observable in the
drift in various degrees. In some places, humus, peat, wood, or other organic
matter occurs between drift s h e e t s . In other places, parts or a l l of a soil, or
weathering, profileare found on a drift sheet; t h e profile c o n s i s t s from top downward of t h e following elements: (1) soil with humus and resistant residual pebble s , (2) clay-enriched subsoil, (3) leached and oxidized drift, (4) oxidized
drift, and (5) unaltered drift (Horberg, 1953, p. 9 ) . The profile indicates progressive weathering and alteration of the drift, with oxidation of iron compounds
and leaching of carbonates advancing more rapidly than the decomposition of
minerals t o c l a y s . A widely noted result of weathering of the drift sheets i s the
occurrence of oxidized brown till over more compact unoxidized blue and gray
till. The buried soils indicated by the effects described above have been named
(table 1) (Willman and Frye, 1970) and commonly have been used a s marker horizons.
Another type of material that characterizes the weathered upper part of
drift s h e e t s i s fine-textured sediment, largely clay, that was washed into shallow
initial depressions in the till plain. This type of deposit, called accretion-gley,
resembles the clay-enriched zone of a weathering profile but was formed by a
different process and does not have great significance a s a time indicator (Frye,
Willman, and G l a s s , 1960, p. 19-20; Willman, Glass, and Frye, 1966).
Holocene (Recent) Deposits
Many of the Holocene deposits (table 1) of Illinois are a result of the reworking or redistribution of glacial deposits. Silts, sands, and gravels are
shifted about by scour and fill i n floodplains (fig. 2). Coarse- t o fine-grained
sediments are deposited a s alluvial fans where tributary streams of relatively
high gradients enter the floodplain of a larger stream. Silts are carried by slopewash t o lower ground and eventually into ponds, lakes, swamps, and streams.
Along Illinois l a k e s , waves and shore currents are forming beach deposits. The
wind has formed dunes in Holocene time, most of them south of Lake Michigan.
Organic matter i s another component of Holocene deposition. Peat,
marl, and driftwood a r e common in present-day floodplains. Many swamps i n t h e
poorly drained morainal a r e a s and on the lake plain of Lake Michigan fill with
water-bearing vegetation and other sediments, forming peat and muck.
The Holocene deposits, compared t o the glacial deposits, constitute a
minor part of the unconsolidated overburden of Illinois.
Rocks Confused with Drift
The classification of shale in the geologic sequence in Illinois i s sometimes misunderstood. Shale, which crops out or occurs a t various depths in wide
T H I C K N E S S AND CHARACTER O F GLACIAL DRIFT
9
a r e a s of Illinois, i s part of t h e bedrock rather than part of the drift. However,
some drillers have considered it drift and t h i s h a s resulted in a misunderstanding
about t h e securing of permits and payment of f e e s t o t h e Department of Mines
and Minerals when water wells a r e t o penetrate t h e subsurface below the drift.
In much of Illinois, where s h a l e s of the Pennsylvanian System form the uppermost bedrock, t h e drift i s l e s s than 50 feet thick. The Geologic Map of Illinois
(Willman and others, l967), which shows t h e distribution of bedrock formations
below the drift, should be examined in conjunction with t h e drift t h i c k n e s s map
(pl. 1) t o determine depth t o bedrock and kind of bedrock. , Where s h a l e s a r e
shown t o constitute a large part of t h e uppermost bedrock, s p e c i a l care i s required t o distinguish drift from bedrock.
THICKNESS OF DRIFT
Method of Study and Extent of Data
The drift t h i c k n e s s map (pl. 1) i s based on four sources of informationwell records, refraction seismic determinations, drift t h i c k n e s s maps from previous a r e a l investigations, and differences in elevation between land surface
and mapped bedrock surface in selected a r e a s where well data a r e s p a r s e or
poorly distributed. Altogether, about 18,600 drift t h i c k n e s s points were used
i n preparing t h e present map. A 25-foot thickness line w a s added t o t h e map i n
revising the 196 7 map (Piskin and Bergstrom, 196 7). The distribution of control
points and t h e a r e a s for which drift t h i c k n e s s maps had previously been prepared
are shown i n figure 3 .
The t h i c k n e s s of drift a t about 16,000 points w a s plotted from key well
records i n t h e f i l e s of the Geological Survey. The records considered most reliable for determination of drift t h i c k n e s s were t h e l o g s of water wells, engineering borings, and c o a l borings; many of t h e s e have drill cuttings t h a t have
been interpreted by Survey personnel. Such records were used a s a key in interpreting other kinds of records. Some data on drift t h i c k n e s s were obtained from
records of o i l w e l l s i n many l o c a l i t i e s i n t h e southern part of the s t a t e . In some
c a s e s , subsurface samples were reexamined t o verify t h e depth of bedrock.
Drift t h i c k n e s s maps for parts of the s t a t e have been made previously by
Geological Survey personnel, chiefly in connection with ground-water investigat i o n s . These maps were incorporated, with modifications a s n e c e s s a r y , i n
plate 1 Some of t h e s e maps a r e a t present unpublished.
In area A (fig. 3 ) , drift t h i c k n e s s maps were presented by Suter e t a l .
(1959) for most of a n eight-county area and by Zeizel e t a1. (1962) for Du Page
County.
Drift t h i c k n e s s maps of Boone and De Kalb Counties (area B) were prepared by John P. Kempton (1968a, b) a s part of a ground-water investigation.
The adjacent area (C) w a s studied by James E . Hackett (1960); in t h i s study 600
well records were used, of which about 200 a r e based on drill samples. Ogle
County (D) w a s studied by Richard R. Parizek (1962).
Area E w a s studied by D. A. Stephenson (1967) relative t o ground-water
geology of part of the Mahomet Bedrock Valley. His drift thickness map, based
largely on water well records, shows contours a t a 50-foot interval. The southern
part of McLean County of Stephenson's map w a s modified in preparing t h e drift
thickness map for t h i s report.
.
10
I L L I N O I S STATE G E O L O G I C A L SURVEY C I R C U L A R 4 9 0
,----
Area in which thickness lines
were modified from previous
reports. Outcrop taken mainly
from Horberg, 1950
Fig. 3
-
Sources of d a t a for drift t h i c k n e s s map (pl. 1). (See page 35 for map
of Illinois showing county names; previous reports on a r e a s indicated
by diagonal pattern a r e cited on pages 9 and 11.)
T H I C K N E S S AND CHARACTER O F GLACIAL DRIFT
A drift thickness map on a 50-foot interval w a s prepared for area F by
Walker, Bergstrom, and Walton (1965). This map w a s adapted for the present
s t a t e map by using only the 50-, loo-, 200-, and 300-foot t h i c k n e s s l i n e s .
For area G, Bergstrom and Walker (1956) presented a drift t h i c k n e s s map
a t a 20-foot contour interval. Some modifications of t h i s map were made i n preparing the present s t a t e map. Similarly, some revisions of a map of White County
(H) by Pryor (195633)were made for t h e s t a t e map. The contouring of Rock Island
County (I) w a s revised from a map prepared by Richard C . Anderson i n 1973.
Drift thickness i n Sangamon, Macon, and extreme northern Christian Counties (J)
w a s adapted from a map for a regional geologic study for planning by Bergstrom,
Piskin, and Follmer (in preparation). The thickness of drift i n St. Clair County
(K) a l s o was adapted from a map for a planning study (Jacobs, 1971).
The other data on drift thickness came from calculated differences in
elevation between land surface and mapped bedrock surface. Approximately
2,500 t h i c k n e s s e s were calculated i n selected a r e a s where well control is s p a r s e .
Land surface elevations were taken from U S Geological Survey quadrangle
topographic maps, and bedrock surface elevations in most of the s t a t e were e s t i mated from Horberg's bedrock topography map (1950, 1957). Most of t h e bedrock
outcrop points were a l s o taken from Horberg's map.
In addition t o Horberg's bedrock surface map, for which data were compiled from a l l Survey reports published before 1950, t h e following bedrock surface maps were used: a n unpublished map of Iroquois, northern Vermilion, and
Ford Counties by Keros Cartwright (1970); a map of area E (fig. 3) by Stephenson
(1967); and a map of the De Witt-McLean County area by Heigold, McGinnis ,
and Howard (19 64)
..
.
Factors Controlling Drift Thickness
Differences in t h e thickness of drift a r e a result of t h e depositional
patterns of t h e i c e , water, and wind t h a t laid down thedrift and of t h e subsequent
erosion of t h e drift by i c e and running water. In a r e a s that were glaciated several times, including t h o s e t h a t were covered by t h e l a t e s t glaciation, t h e Wisconsinan, thicker drift accumulated. In a r e a s outside the Wisconsinan drift
plain (fig. l ) , t h e drift i s thinner, for there were fewer and older glaciations and
there h a s been time s i n c e t h e l a s t (Illinoian) i c e melted for extensive weathering
and erosion t o occur. The thickening of the drift from south t o north and from
west t o e a s t is illustrated by t h e cross-sections o n p l a t e 2 and by t h e drift thickn e s s map (pl 1 ) . For example, cross-section F-F' i n plate 2 shows t h e drift
a c r o s s the Illinoian t i l l plain in t h e southern part of t h e s t a t e t o be thin i n cont r a s t t o t h e thick drift of the Wisconsinan ridged plain in t h e northern part (crosssection B-B').
In cross-section E-E', t h e thin Illinoian drift is on the left, t h e
Shelbyville Moraines marking the Wisconsinan front are near the middle, and t h e
thicker drift below the Wisconsinan drift plain is on t h e right.
The patterns of drift t h i c k n e s s shown i n plate 1 reflect irregularities a t
the b a s e of the drift (the bedrock surface) or a t t h e top of the drift (present land
surface), or both. An intricate erosion surface with valleys and uplands w a s developed on t h e uppermost bedrock before and during glacial t i m e s , with t h e result
that t h e drift was deposited on a very uneven floor. The glaciers themselves
fashioned many landforms, such a s end moraines, kames, and e s k e r s , t h a t make
.
,
I L L I N O I S STATE G E O L O G I C A L SURVEY C I R C U L A R
t h e upper surface of t h e drift uneven; and i n some a r e a s erosion h a s produced
further irregularities. The cross-sections (pl. 2) show t h a t of t h e two surfaces
involved-bedrock
surface and pre s e n t land surface -the bedrock surface ha s
greater gross relief; t h e drift mantle h a s somewhat subdued t h e older topography.
In general, then, drift t h i c k n e s s and t h e pattern of thickness l i n e s reflect mainly
the bedrock topography.
Drift i n Bedrock Valleys
Horberg's report (1950) on t h e bedrock topography of Illinois delineated
the main valleys and upland surfaces and described t h e character of t h e drift fill
i n the valleys. The bedrock valley systems shown i n figure 4 a r e taken basically
from Horberg % report.
Comparison of plate 1 (generalized in fig. 5) with figure 4 and t h e crosssections (pl. 2) shows that the a r e a s of thickest drift correspond t o the Princeton, Pawpaw, Troy, Middle Illinois, Mackinaw, Danvers, and Mahomet Bedrock
Valleys and their tributaries. With t h e exception of the Middle Illinois, t h e s e
valleys a r e almost completely buried by glacial drift and d o not conform with
present drainage l i n e s . Where moraines (fig. 1) c r o s s buried valleys or are a ligned with them, t h e drift i s further thickened. Drift thickness in the major
buried bedrock valleys and i n related present valleys and lowlands is summarized below.
Princeton Bedrock Valley
The Princeton Bedrock Valley carried t h e Ancient M i s s i s sippi River e a s t ward t o t h e valley of the present Illinois River before being closed by drift deposited i n Wisconsinan time, when t h e M i s s i s s i p p i assumed i t s present more westerly
course. The valley underlies t h e Green River Lowland on the west and t h e Wisconsinan drift plain on t h e e a s t (C-C', pl. 2 ) . The valley i s about 65 miles long
and 3 t o 7 miles wide.
In t h e Green River Lowland, t h e drift averages 160 feet i n t h i c k n e s s , but
over a deep bedrock channel i n t h e middle of the Lowland, it probably a t t a i n s a
thickness of 225 f e e t . At Erie, a mile south of t h e deep channel, bedrock w a s
reached a t 167 f e e t . Where t h e bedrock valley p a s s e s under the Bloomington
Morainic System and t h e Eureka-Dover Moraines, .in central Bureau County, the
drift averages 300 feet i n thickness and a t t a i n s a maximum t h i c k n e s s of more
than 400 f e e t . A well a t Princeton reached bedrock a t 372 f e e t .
Upper Rock River, Troy, and Pawpaw Bedrock Valleys
The Upper Rock River Bedrock Valley includes the bedrock v a l l e y system
s t i l l followed by present drainage north of the Harrisville Moraine. From the
point i n southeastern Ogle County a t which t h e bedrock valley p a s s e s southward
under the Bloomington Moraines, i t is known a s Pawpaw Bedrock Valley. Troy
Bedrock Valley, in Boone and De Kalb Counties (A-A' , pl. 2 ) , parallels t h e Upper
Rock and Pawpaw Valleys, then joins Pawpaw Valley in southeastern Lee County.
Pawpaw Valley joins Princeton Valley in Bureau County, in the vicinity of
Princeton.
The Upper Rock River Bedrock Valley i n Illinois i s nearly 45 miles long
and from 1$ t o 3 i miles wide. The t h i c k n e s s of the drift ranges from 150 t o 400
T H I C K N E S S AND CHARACTER O F GLACIAL DRIFT
13
feet and averages 200 f e e t . At Rockford, wells commonly reach bedrock a t
depths of more than 200 feet. In Pecatonica River Valley, the drift averages
125 feet in thickness and a t t a i n s a maximum of more than 250 feet.
Pawpaw Bedrock Valley is about 45 miles long and up t o 8 miles wide.
The drift i s mainly 350 t o 550 feet thick (B-B', pl. 2) and i n a few p l a c e s i s
probably 600 f e e t thick. The t h i c k e s t drift in t h e s t a t e is found i n southeastern
Lee County, where the Bloomington Moraines c r o s s Pawpaw Bedrock Valley. At
Pawpaw, bedrock is-reached a t a depth of about 450 f e e t . The nature of t h e
drift in t h e lower Pawpaw Valley i s illustrated by the log of well 6 (appendix).
Troy Bedrock Valley i s completely filled by drift, except for a few.miles
i n southwestern Boone and southeastern Winnebago Counties where i t i s occupied by t h e Kishwaukee River. The valley is 60 miles long and 1$ t o 3 miles
wide (McGinnis, Kempton, and Heigold, 1963). In southern De Kalb County,
the drift e x c e e d s 400 feet i n t h i c k n e s s , and i n northeastern Boone and northwestern McHenry Counties, it may be 500 feet thick. A core boring drilled for
the Northeastern Illinois Metropolitan Area Planning Commission in s e c 7, T
46 N., R. 5 E., i n northwestern McHenry County (Lund, 1965, p . 43-52) p a s s e d
through a typical Wisconsinan till and gravel sequence (well 7, appendix) and
reached bedrock a t about 474 f e e t .
.
.
Ticona Bedrock Valley
Ticona Bedrock Valley joins Princeton Bedrock Valley just e a s t of Hennepin, Putnam County, and i s entirely buried eastward t o t h e western boundary of
Grundy County. The drift a t t a i n s a thickness of more than 200 feet (B-B' , pl 2 ) .
.
Newark Bedrock Valley
Newark Bedrock Valley, of Kane, Kendall, and Grundy Counties, may
have carried t h e headwaters of Kempton Bedrock Valley of Livingston and Grundy
Counties. Newark Valley is about 1 mile wide and is entirely buried by drift
ranging from 50 t o approximately 200 feet i n t h i c k n e s s (C-C', pl. 2 ) .
Illinois Valley
From Hennepin southward, t h e Illinois River flows in a n alluviated bedrock valley t h a t is composed of segments of different a g e s and h a s various thickn e s s e s of fill. The Middle Illinois Bedrock Valley, between Hennepin and Peoria,
i s about 35 miles long and about 7 miles wide, whereas t h e present Illinois River
Valley is about 4 miles wide (C-C', pl. 2 ) . The western bluff of t h e river coinc i d e s with t h e western edge of t h e bedrock valley. Drift beneath t h e river floodplain a t t a i n s a maximum t h i c k n e s s of 200 f e e t , whereas beneath the upland, over
the bedrock channel e a s t of t h e river, t h e drift i s up t o 350 feet thick.
Just north of Peoria, t h e wide, d e e p bedrock valley a n g l e s southeast
beneath t h e upland, where it is called Mackinaw Bedrock Valley. The Illinois
River continues south, first p a s sing through a narrow, shallow bedrock gorge
between Peoria and East Peoria and t h e n following a slightly wider bedrockchannel (Pekin-Sankoty) t h a t diverges from t h e main bedrock valley just north of
Peoria and p a s s e s under western Peoria and p a s t Pekin t o the Havana Lowland.
The channel i s 2 t o 3 miles wide, i n places underlies t h e upland, and i n places
underlies t h e present floodplain.
Within the narrow gorge between Peoria and East Peoria, the drift-outwash and Holocene alluvium-attains a t h i c k n e s s of 100 f e e t . Over t h e Pekin-
14
ILLINOIS STATE G E O L O G I C A L SURVEY CIRCULAR 490
2
0
10
20
30
40MILES
Fig. 4 - Axes of present valleys and bedrock valleys.
THICKNESS AND CHARACTER OF GLACIAL DRIFT
Fig. 5 - Generalized drift t h i c k n e s s in Illinois
.
15
16
I L L I N O I S STATE G E O L O G I C A L SURVEY C I R C U L A R 4 9 0
Sankoty Bedrock Channel, glacial deposits may reach a thickness of 400 feet
under the present upland and are about 120 feet thick below the present floodplain.
South of Pekin, t h e Illinois River c r o s s e s the western part of a wide lowland. Here the drift ranges from l e s s than 50 feet in thickness beneath t h e floodplain, west of the river, t o more than 200 feet e a s t of the river, where river terraces with sand dunes overlie the deepest part of the bedrock valley (D-D', pl. 2 ) .
Where the Illinoian and Wisconsinan drift uplands, which contain l o e s s deposits,
overlie t h e deep part of the bedrock valley, the drift reaches 400 feet in thickness.
The Illinois River Bedrock Valley becomes progressively narrower south
of the Havana Lowland, decreasing from 6 miles in width a t Beardstown t o slightly
more than 2 miles in width a t t h e mouth of the river. The average thickness of the
fill in the valley i s 125 feet, and the maximum i s about 175 feet.
Mackinaw Bedrock Valley
The Mackinaw Bedrock Valley i s 5 t o 10 miles wide and extends from
western Woodford County t o southern Tazewell County, where it joins the Mahomet Bedrock Valley. Between 300 and 500 feet of drift overlies t h e valley. At
Washington, Tazewell County, a well over the valley reached bedrock a t 3 70
feet. At Mackinaw, Tazewell County, a well reached bedrock a t 380 feet.
Danvers Bedrock Valley
The Danvers Bedrock Valley, an east- side tributary of Mackinaw Valley,
i s from 3 t o 9 miles wide in Living ston, Woodford, and Tazewell Counties and
is overlain by 100 t o more than 400 feet of drift.
Mahomet Bedrock Valley
The Mahomet Bedrock Valley and i t s tributaries are well defined by belts
of thick drift in east-central Illinois. Originally described by Horberg (1945,
1950), the Mahomet Valley enters Illinois a t t h e northeastern corner of Vermilion
County and joins t h e Mackinaw Bedrock Valley i n southern Tazewell County. The
a x e s of t h e valley and i t s tributaries, shown in figure 4, are essentially from
Horberg (1950, pl. 2), with modifications by Cartwright (1970); Heigold, McGinn i s , and Howard (1964); and Stephenson (1967). The chief modification i s t h e
movement of the valley a x i s eastward 5 or 6 miles in De Witt County. The modifications are based on additional subsurface data and on seismic investigations.
The Mahomet Valley i s about 135 miles long in Illinois, and the belt of
thick drift (300 feet or more) over t h e valley i s a t l e a s t 3 miles wide and locally
up to 10 miles wide (B-B', E-E', pl. 2 ) . The maximum thickness of drift penetrated in a well t o date i s 447 f e e t a t Paxton, Ford County. Thick drift (more
than 400 feet) i s found i n t h e vicinities of Hoopeston and Rankin in Vermilion
County, Kenney in De Witt County, and Mahomet in Champaign County, where
moraines cross the bedrock valley. In the eastern part of the valley, the drift
may attain a thickness of 500 feet. Typical deposits of t h e Mahomet Valley are
illustrated by the log of well 4 (appendix).
Kempton-Chat sworth-Onarga Bedrock Valleys
the
em
the
the
The Kempton-Chatsworth-Onarga Bedrock Valleys, a tributary system of
Mahomet, localize belts of thicker drift in Iroquois, northern Ford, and eastLivingston Counties. At t h e junction of t h e Kempton and Mahomet Valleys,
drift i s more than 400 feet thick, whereas up valley in the three tributaries,
drift i s more than 200 feet thick.
T H I C K N E S S AND CHARACTER O F GLACIAL DRIFT
17
Middletown Bedrock Valley
The position of t h e lower course of the Middletown Bedrock Valley (fig.
4) i s modified from Walker, Bergstrom, and Walton (1965) rather t h a n Horberg
The Middletown Valley and a tributary, Athens Bedrock Valley, a r e s i t e s of
thicker drift i n Menard, Logan, Sangamon, Christian, Macon, and Moultrie
Counties (D-D\ pl 2). Wells a t Middletown, i n western Logan County, a r e
about 150 feet d e e p and are finished i n sand and gravel on the western flank of
the Middletown Valley. Farther e a s t , over the a x i s of the valley, the drift a t t a i n s a t h i c k n e s s of more t h a n 200 feet.
.
.
Present Drainages
The M i s s i s s i p p i , Kaskaskia, Big Muddy, Wabash, Embarras , Little
Wabash, Ohio, and Cache River Valleys generally contain thicker unconsolidated deposits than t h e regions t h e y c r o s s .
Deposits i n t h e bedrock channel of the M i s s i s s i p p i Valley north of
Princeton Valley range i n t h i c k n e s s from about 140 feet t o possibly more than
300 feet, t h e average being more t h a n 150 f e e t . A t h i c k n e s s of 340 feet is reported by Horberg (1950, p. 46) for a well a t Dubuque, Iowa, a c r o s s t h e river
from t h e northwestern corner of Illinois. In t h e M i s s i s s i p p i Valley, between
Princeton Valley and t h e mouth of t h e Illinois River, the d e p o s i t s have a n avera g e t h i c k n e s s of 150 feet and locally a r e more than 200 feet thick. In several
places (fig. l ) , t h e river i s directly against t h e bluff and a t t h e s e p l a c e s there i s
e s s e n t i a l l y no floodplain in Illinois. The fill i n the M i s s i s s i p p i Valley south of
the Illinois River ranges i n t h i c k n e s s from 125 feet t o more than 170 f e e t . In t h e
American Bottoms, in Madison County, the valley fill e x c e e d s 170 feet in thickn e s s below a terrace a t Wood River (F-F' , pl. 2) (Bergstrom and Walker, 1956).
Deposits i n t h e Kaskaskia and Big Muddy Valleys reach t h i c k n e s s e s of
125 feet (F-F', pl. 2). The bedrock valleys d o not conform t o t h e present vall e y s i n a l l c o u r s e s of t h e streams.
Deposits i n the Wabash Valley a r e 100 t o 150 feet thick. In a long
stretch of the Embarras Valley and i n portions of the Little Wabash River Valley,
t h e y a r e more than 100 feet thick.
Approximately 25 miles south of the Illinoian drift border, t h e Cache Bedrock Valley, a former course of t h e Ohio River, contains a s much a s 160 feet of
pebbly sand. The valley fill of the Ohio and M i s s i s s i p p i Rivers a t t h e very
southern t i p of t h e s t a t e i s a s much a s 250 feet thick (Pryor and Ross, 1962).
The alluvial d e p o s i t s in the Black Bottom area of the Ohio River floodplain i n
the southeastern part of t h e s t a t e are up t o 100 feet thick (Ross, 1964).
Drift on Bedrock Uplands
The drift on t h e bedrock uplands i n wide s t r e t c h e s of northwestern, weste m , and southern Illinois i s l e s s than 50 feet thick. In many places-on hills i d e s , in river bluffs, or in tributary creek beds or ravines-the drift h a s been
removed by erosion, exposing bedrock. The a r e a s of thin, eroded drift of weste m and southern Illinois (fig. 5) approximately coincide with the Illinoian drift
plain (fig. 1 ) .
Within the Wisconsinan drift plain, thin eroded drift overlies t h e bedrock
uplands i n northwe stern Illinois and i n La Salle, Living ston, Kendall, Grundy ,
Will, and Kankakee Counties. Fairly thick drift, commonly 100 feet thick or
18
I L L I N O I S STATE G E O L O G I C A L SURVEY C I R C U L A R 4 9 0
more, overlies the bedrock uplands i n e a st-central and northeastern Illinois.
As shown by t h e cross-sections (pl, 2 ) , drift more than 100 feet thick over bedrock upland s usually occurs only where moraine s a r e present.
Surficial Features
In addition t o reflecting features of the bedrock surface, the drift thickn e s s map shows some of t h e moraines, terraces, and dunes and many of t h e
drainage l i n e s of t h e present landscape The thickening of t h e drift t o more than
50 feet i n east-central Illinois marks the Shelbyville Moraines. The Valparaiso
and Lake Border Moraines i n northeastern Illinois are marked by belts of drift
from 100 t o more than 200 feet thick. Small, closed, irregular t h i c k n e s s l i n e s ,
showing 200 and 300 feet of drift i n Mason County, reflect dunes on terraces
and on the drift plain of t h e Havana Lowland. If data were available, additional
closed contours showing l o c a l thickening of drift would probably be shown adjacent t o the Illinois and M i s s i s s i p p i Valleys where thick d e p o s i t s of l o e s s
occur.
The present major drainages-such a s the M i s s i s s i p p i and lower Illinois
Rivers-are accentuated by bands of rock outcrops along linear belts of thicker
drift. Many of the smaller tributary streams a r e marked by dendritic belts of
rock outcrop, showing t h a t t h e y a r e flowing on rock with e s s e n t i a l l y no f i l l . The
course of the lower Des Plaines River i s marked in t h i s fashion.
.
CHARACTER OF DRIFT
Wisconsinan Deposits
Deposits of t h e Wisconsinan Stage (table 1) a r e the uppermost earth
materials in much of Illinois. The most prominent area of Wisconsinan deposits is the ridged plain north of Shelbyville and e a s t of Peoria (fig. 1) t h a t
includes almost 100 named end moraines (Willman and Frye, 1970). These deposits average 75 t o 100 feet in t h i c k n e s s and a t t a i n a maximum t h i c k n e s s of
about 250 feet (Horberg, 1953, pl 1). They c o n s i s t e s s e n t i a l l y of t i l l s , with
some l o e s s , l a k e sediments, and outwash, and a r e divided into formations and
members on the b a s i s of physical characteristics. The log of well 1 (appendix)
in Lake County illustrates a fairly typical Wisconsinan sequence in northeastern
Illinois
The Wisconsinan t i l l s a r e generally l e s s compact, lighter i n color, and
have a shallower profile of weathering than the older glacial deposits; the average depth of leaching is about 3 feet (Horberg, 1953, p. 38). In subsurface,
there i s l e s s outwash a s s o c i a t e d with t i l l s h e e t s than i n t h e Illinoian d e p o s i t s .
Pebbles constitute 1 or 2 percent t o more t h a n 80 percent of the t i l l s and commonly constitute 5 t o 10 percent (Krumbein, 1933; Anderson, 1955, 1957). The
t i l l s range i n texture from c l a y e y t o sandy and gravelly (Krumbein, 1933; Willman, Payne, and Voskuil, 1942; Bretz, 1955; Horberg and Potter, 1955; Shaffer,
1956; Kempton, 1963; Frye, G l a s s , and Willman, 1969; Johnson e t a l . , 1971).
Extensive data reported by Willman and Frye (1970) show t h a t the matrix of t h e
Wisconsinan t i l l s t e n d s t o be clayey t o s i l t y rather than sandy. Data on the
physical, chemical, and engineering properties of t h e surficial d e p o s i t s of t h e
region a r e given by Wascher e t a1 (1960) and Thornburn (1963).
.
.
.
T H I C K N E S S AND CHARACTER O F GLACIAL D R I F T
Outwash, ranging from gravel t o s i l t , occurs in valleys that p a s s through
and beyond the Wisconsinan drift border and in outwash plains that border moraines. Two of the largest outwash a r e a s , the Green River-lower Rock River basin
(Leighton, Ekblaw, and Horberg, 1948, p. 25) and t h e Havana region of t h e Illinois River (Walker, Bergstrom, and Walton, 1965), contain sand and gravel deposi t s that are essentially continuous t o bedrock (fig. 1; p l . 2); but in t h e s e a r e a s
there i s a l s o fine-grained Holocene alluvium along present streams. The log of well
2 (appendix) illustrates the sand and gravel sequence near Havana. The Kaskaskia, Little Wabash, and Embarras Rivers (figs. 1 and 4) a l l contain valley-train
deposits that head within the Wisconsinan drift plain and become finer downstream. Horberg (1950) describes the outwash of the valley systems.
Much glaciofluvial sand and gravel i s present in t h e form of outwash
plains, valley trains, and kames i n McHenry and Kane Counties i n northeastern
Illinois (Ekblaw and Lamar, 1964). The deposits here overlie fairly thick t i l l .
The occurrence and nature of other surficial and shallow sand and gravel deposi t s of Wisconsinan age are described in county sand and gravel resource reports
and in quadrangle and other regional geologic reports. Anderson described t h e
sand and gravel resources i n Champaign (1960) and De Kalb (1964) Counties and
along the Rock River (1967). Anderson and Block reported on McHenry County
(1962); Anderson and Hunter, on Peoria County (1965); Block, on Kane County
(1960); Hunter, on Tazewell County (1966); Hunter and Kempton, on Boone County
(1967); Hester, on Sangamon County (1970); and Hester and Anderson, on Macon
County (1969). Willman and Frye (1969) reported on high-level outwash in northwe stern Illinois. In 1923, Bretz reported on t h e geology and mineral resources of
the Kings Quadrangle, and in 1939, he described the geology of the Chicago
region. Willman, Payne, and Voskuil (1942) described the geology and mineral
resources of the Marseilles, Ottawa, and Streator Quadrangles. The Beardstown,
Gla sford, Havana, and Vermont Quadrangles were covered by Wanless (1957).
The geology of the Buda Quadrangle was described by MacClintock and Willman
(1959). Willman (1971) summarized the geology of northeastern Illinois.
The occurrence of deeper outwash of Wisconsinan age and older i s described in reports that d e a l primarily with ground water. Horberg (195 0) described
the bedrock topography of Illinois and later (1953) t h e Pleistocene deposits below
the Wisconsinan drift in northeastern Illinois. Bergstrom e t a l . (1955) described
ground-water possibilities i n northeastern Illinois, and Suter e t a l . (1959) described ground-water resources of the Chicago region. Hackett and Bergstrom
(19 56) reported on ground water in northwe stern Illinois ; Selkregg and Kempton
(19 58 ) , on ground water in east-central Illinois; Bergstrom (1956) and Bergstrom and
Zeizel (1957), on ground water in western Illinois ; Selkregg , Pryor, and Kempton
(1957), on ground water in south-central Illinois; and Pryor (1956a), on ground water
in southern Illinois. Ground-water resources of Du Page County were described by
Zeizel e t a l . (1962). Foster (1956) described the ground-water geology of Lee and
White side Counties Hackett (1960) reported on Winnebago County, and the groundwater geology of White County w a s described by Pryor (1956b). Walker, Bergstrom,
and Walton (1965) described ground-water resources of the Havana region. The East
St. Louis area was described by Bergstrom and Walker (1956) Horberg, Suter, and
Larson (1950) described ground water in the Peoria region, and Foster and Buhle
(1951) investigated aquifers in glacial drift near Champaign-Urbana
Wisconsinan l o e s s i s widespread in Illinois and constitutes the parent
materials of the modern soils i n much of the s t a t e . Where viewed in road c u t s
or river bluffs, it usually appears a s massive yellowish t o reddish brown s i l t
.
.
.
20
I L L I N O I S STATE G E O L O G I C A L SURVEY C I R C U L A R 4 9 0
t h a t stands i n s t e e p vertical f a c e s . It i s thickest and coarsest on the lee s i d e s
of t h e Mississippi, Illinois, Green, and Ohio Rivers (fig. 1; Smith, 1942 [fig.
3]), especially adjacent t o t h e wider stretches of valley flat. For example, e a s t
of the wide American Bottoms a t East St. Louis the l o e s s i s about 70 feet thick,
and in C a s s County, adjacent t o the broad valley a t Havana, the l o e s s i n a few
places i s more than 90 feet thick. The l o e s s decreases rapidly in thickness and
coarseness within 2 or 3 miles of the river bluffs, then thins and gradually becomes finer grained. In much of Illinois, the l o e s s i s only a few feet thick.
Along the river bluffs, where the l o e s s i s thick, i t i s commonly calcareous and
contains small fossil snail s h e l l s . Away from the valley, where the l o e s s thins,
it i s usually leached and unfossiliferous
The l o e s s c o n s i s t s of a distinct succession of deposits that have been
intensively studied (Smith, 1942; Leighton and Willman, 1950; Frye and Willman,
1960; Leonard and Frye, 1960; and Frye, G l a s s , and Willman, 1962, 1968).
.
Illinoian Deposits
Illinoian deposits with a cover of Wisconsinan l o e s s vary in thickness
and extend into southern Illinois t o about 8 or 10 miles south of Carbondale
and into western Illinois approximately t o the Mississippi River (fig. 1). Illinoian drift has been traced beneath the Wisconsinan drift of northeastern Illinois
for many miles (Horberg , 1953, p 2 6)
Several Illinoian moraines occur in the western part of the state (fig. l ) ,
but no continuous end moraine developed a t t h e border of the Illinoian drift. The
Illinoian i s characterized by a relatively high proportion of outwash and by hard,
silty, brownish gray or dark gray t i l l s . The log of well 3 (appendix) in Montgomery County illustrates the nature of the Illinoian drift.
At the top of the Illinoian t i l l the intensely weathered zone i s a s much
a s 6 feet thick and averages about 2 feet. The t i l l i s leached t o a depth of 5 t o
12 feet, with a n average of about 8 f e e t , and the oxidized zone extends down t o
12 t o 15 feet below t h e surface (Horberg, 1953, p 28). A very clayey deposit,
called accretion-gley, that accumulated in low places on the till plain i s common in many a r e a s . Where Wisconsinan and Illinoian t i l l s c a n be compared in
one exposure, the Illinoian till i s much more compact and jointed. Beds of sand
and gravel are common a t t h e base, i n t h e middle, and a t t h e top of the Illinoian
deposits.
Data on the texture and mineralogy of the Illinoian t i l l s are given by
Horberg (195 6) ; Frye , Willman, and Gla s s (19 60) ; Willman, Gla s s , and Frye
(1963, 1966); and Willman and Frye (1970) Descriptions of the Illinoian deposi t s in various a r e a s of Illinois are given by Horberg, Suter, and Larson (1950);
Foster and Buhle (195 1); Pryor (19 56a) ; Wanless (1957); Johnson (1964); Jacobs
and Lineback (1969); Frye, G l a s s , and Willman (1969); Johnson (1971); and
Johnson e t a1 . (19 7 1)
. .
.
.
.
Pre-Illinoian Deposits
Pre-Illinoian deposits are irregularly distributed in Illinois. Their extent i s not well known, and, where present, they are usually overlain by younger
drift. Only in western Hancock, Adams, and Pike Counties does the older driftthe Kansan-emerge from beneath the outer edge of the Illinoian (fig. 1).
T H I C K N E S S AND CHARACTER O F GLACIAL DRIFT
The older drifts a r e usually identisied by weathered zones a t their t o p s
and by their occurrence below the Illinoian drift. They are commonly dark colored, oxidized, and d e n s e and frequently contain wood fragments and peaty material. The mineralogy of t h e pre-Illinoian drift h a s been studied by Willman,
G l a s s , and Frye (l963), and a r e a l descriptions of t h e Kansan d e p o s i t s a r e given
by Horberg (1956), W a n l e s s (1957), Johnson (1964, l 9 7 l ) , and Willman and Frye
(1969, 1970).
In the Champaign-Urbana a r e a , and extensively along the Mahomet Bedrock Valley, the Kansan d e p o s i t s c o n s i s t of yellow-brown t o gray, pebbly, s i l t y
t i l l underlain by thick beds of sand and gravel t h a t extend t o bedrock. The thickn e s s of the sand and gravel ranges up t o about 150 feet (Foster and Buhle, 1951,
p. 381-383). Horberg (1953, p. 18) applied t h e name "Mahomet Sand" t o the
thick sand and gravel beds overlying bedrock in the Mahomet Bedrock Valley (pl.
2) and considered them similar i n a g e and origin t o t h e Sankoty Sand of t h e Ancient M i s s i s sippi Valley. The log of well 4 (appendix) i l l u s t r a t e s the nature of
the Mahomet Sand and overlying Illinoian and Wisconsinan d e p o s i t s i n t h e
Mahomet Valley in Champaign County.
The Sankoty Sand (Horberg, 1950, p . 34-36) i s a continuous fill along
the Ancient M i s s i s s i p p i Valley (pl 2 ) and h a s been recognized in cuttings from
wells a s far south a s Havana i n Mason County and a s far north a s Prophetstown
i n southern Whiteside County (Horberg, 1953, p. 13-18). The sand i s
commonly medium grained, but the d e p o s i t s range from fine-grained s i l t y sand
t o coarse-grained gravelly beds. The t h i c k n e s s of t h e sand varies greatly; the
maximum thickness may be almost 300 f e e t , but the average is c l o s e r t o 100
feet. The position and nature of the Sankoty Sand i n Mason and Bureau Counties
are illustrated in logs 4 and 5 (appendix).
The Sankoty and Mahomet Sands a r e economically t h e most important
Kansan d e p o s i t s , for they constitute one of t h e most prolific aquifer systems in
Illinois, providing water for many towns and industries in a part of the s t a t e
where no other highly permeable aquifers a r e present.
The Nebraskan glacier invaded western Illinois, but i t s d e p o s i t s have
been s o extensively eroded t h a t t h e extent of t h e area it covered i s highly indefinite. Nebraskan deposit s probably constitute a n insignificant part of t h e
drift mantle of Illinois.
Some sand, gravel, and c l a y d e p o s i t s up t o 100 feet thick i n Adams and
Pike Counties, e a s t of Quincy (fig. 5) , have been interpreted a s Cretaceous i n
age (Frye , Willman, and G l a s s , 1964). They differ markedly in mineralogy
from the glacial d e p o s i t s .
.
CONCLUSIONS
The t h i c k n e s s and character of drift in Illinois have practical implications
for individual, industrial, and administrative i n t e r e s t s i n the s t a t e . In t h i s report
we have summarized t h e main features of t h e drift. We have shown that t h e
drift includes many kinds of earth materials and varies i n character and thicknes s from place t o place. Geologically speaking, t h e s e materials are relatively
young and were formed on land, a s opposed t o t h e layered (and usually cemented
or consolidated) bedrock that underlies the drift, t h a t i s many millions of years
older than t h e drift, and t h a t w a s formed from sediments deposited in or c l o s e
t o t h e s e a . Shale is part of the bedrock, not of the drift.
22
I L L I N O I S STATE G E O L O G I C A L SURVEY C I R C U L A R 4 9 0
The drift is thin and t h e bedrock is widely exposed in southern and western Illinois and t h e part of northeastern Illinois adjacent t o t h e Illinois, Des
Plaines, and Kankakee Rivers. These a r e a s may be of s p e c i a l interest t o indust r i e s t h a t quarry limestone, sandstone, or s h a l e , or t h a t mine c o a l . The Geologic Map of Illinois shows t h e nature of t h e bedrock.
Public health officials have different i n t e r e s t s in t h e thickness and nature of the drift and t h e kind of bedrock directly below. For example, where
limestone or dolomite i s t h e uppermost bedrock, crops out extensively, and i s
only partly covered by thin drift, there a r e opportunities for pollutants t o enter
the ground-water reservoir and travel for considerable d i s t a n c e s through joints
and channels. Furthermore, burial of w a s t e s in t h e s e a r e a s introduces t h e
danger of pollution.
Thin drift and extensive rock outcrop, a s opposed t o thick drift, c r e a t e
some problems i n highway and building location and construction. Drift thickn e s s is a l s o of interest t o t h e drilling industry, particularly with regard t o s e t ting surface c a s i n g .
In Illinois t h e drift is t h i c k e s t i n t h e present major river valleys, i n
buried bedrock valleys, and regionally i n t h e northeastern quarter, which w a s
covered by t h e Wisconsinan glacier. The drift i s more than 200 f e e t thick in
some of t h e major valleys and beneath some of t h e moraines and a t t a i n s a maximum t h i c k n e s s of some 600 feet i n t h e Pawpaw Bedrock Valley in southeastern
Lee County.
The a r e a s of thicker drift, which a r e commonly situated along valleys
where glacial meltwater deposited sand and gravel, a r e the most favorable a r e a s
for developing ground-water supplies. In most of t h e southern two-thirds of the
s t a t e , where t h e bedrock yields only modest supplies of ground water, t h e drift
i n bedrock valleys is t h e only source of large supplies, such a s t h o s e required
for municipalities, industries, and irrigation.
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Smith, G . D . , 1942, I l l i n o i s l o e s s : U n i v e r s i t y of I l l i n o i s A g r i c u l t u r a l Experiment S t a t i o n
B u l l e t i n 490, p. 139-184.
Stephenson, D . A . , 1967, Hydrogeology of g l a c i a l d e p o s i t s of t h e Mahomet Bedrock V a l l e y i n
e a s t - c e n t r a l I l l i n o i s : I l l i n o i s Geological Survey C i r c u l a r 409, 5 1 p.
S u t e r , Max, R . E . Bergstrom, H. F. Smith, G . 11. Emrich, W . C . Walton, and T . E. Larson,
1959, P r e l i m i n a r y r e p o r t on ground-water r e s o u r c e s of t h e Chicago r e g i o n , I l l i n o i s :
I l l i n o i s Geological Survey and I l l i n o i s Water Survey Cooperative Ground-Water
Report 1, 89 p.
Thornburn, T . H . , 1963, S u r f a c e d e p o s i t s of I l l i n o i s - A guide f o r s o i l e n g i n e e r s : U n i v e r s i t y
of I l l i n o i s Engineering Experiment S t a t i o n C i r c u l a r 8 0 , p. 135.
Walker, W . H . , R . E . Bergstrom, and W . C . Walton, 1965, P r e l i m i n a r y r e p o r t on t h e groundwater r e s o u r c e s of t h e Havana r e g i o n i n w e s t - c e n t r a l I l l i n o i s : I l l i n o i s Geologic a l Survey and I l l i n o i s Water Survey Cooperative Ground-Water Report 3 , 61 p.
Wanless, H. R . , 1957, Geology and mineral r e s o u r c e s of t h e Beardstown, G l a s f o r d , Havana,
and Vermont Quadrangles: I l l i n o i s Geological Survey B u l l e t i n 82, 233 p.
Wascher, H . L . , J. D . Alexander, B. W . Ray, A . H . Beavers, and R. T. Odell, 1960, C h a r a c t e r i s t i c s of s o i l s a s s o c i a t e d with g l a c i a l t i l l s i n n o r t h e a s t e r n I l l i n o i s : U n i v e r s i t y
of I l l i n o i s A g r i c u l t u r e Experiment S t a t i o n B u l l e t i n 665, 156 p.
Willman, H. B . , 1971, Summary of t h e geology of t h e Chicago a r e a : I l l i n o i s Geological
Survey C i r c u l a r 460, 77 p.
Willman, H. B . , and J . C . F r y e , 1969, High l e v e l g l a c i a l outwash i n t h e D r i f t l e s s Area of
northwestern I l l i n o i s :
I l l i n o i s Geological Survey C i r c u l a r 440, 23 p.
Willman, H. B., and J . C . F r y e , 1970, P l e i s t o c e n e s t r a t i g r a p h y of I l l i n o i s : I l l i n o i s
Geological Survey B u l l e t i n 94, 204 p.
Willman, H. B., and o t h e r s , 1967, Geologic map of I l l i n o i s : I l l i n o i s Geological Survey
map ( s c a l e l:5OO,OOO).
Willman, H. B., H. D . G l a s s , and J. C . F r y e , 1963, Mineralogy of g l a c i a l t i l l s and t h e i r
weathering p r o f i l e s i n I l l i n o i s - P a r t
I. G l a c i a l t i l l s : I l l i n o i s Geological
Survey C i r c u l a r 347, 55 p.
Willman, H. B. , H. D . G l a s s , and J . C F r y e , 1966, Mineralogy of g l a c i a l t i l l s and t h e i r
11. Weathering p r o f i l e s : I l l i n o i s Geoweathering p r o f i l e s i n I l l i n o i s - P a r t
l o g i c a l Survey C i r c u l a r 400, 76 p.
.
26
I L L I N O I S STATE G E O L O G I C A L SURVEY CIRCULAR 4 9 0
Willman, H. B . , A. B. Leonard, and J. C . F r y e , 1971, Farmdalian l a k e d e p o s i t s i n n o r t h e r n
I l l i n o i s : I l l i n o i s Geological Survey C i r c u l a r 467, 12 p.
Willman, H. B . , J. N . Payne, and W. H. Voskuil, 1942, Geology and m i n e r a l r e s o u r c e s of t h e
M a r s e i l l e s , Ottawa, and S t r e a t o r Quadrangles: I l l i n o i s Geological Survey B u l l e t i n
66, 388 p.
Z e i z e l , A . J . , W . C . Walton, R . T . Sasman, and T . A. P r i c k e t t , 1962, Ground-water r e s o u r c e s
of Du Page County, I l l i n o i s : I l l i n o i s Geological Survey and I l l i n o i s Water Survey Cooperative Ground-Water Report 2 , 103 p.
APPENDIX
Logs of Representative Wells
1 . Austin (Deep Freeze) No. 1 , 1951, S E ~ S W ~ S
s eEc .~ 18, T. 44 N . , R. 12 E.,
Lake County. Elevation E.T. M . * 678 feet. Sample s e t 21463. Studied
by P. M . Busch.
Thickness
(ft
Depth t o b a s e
(fi)
Pleistocene Series
Wisconsinan Stage
Wedron Formation
Soil, sandy, black, with organi c fragments
Till, clayey, yellowish orange
Till, calcareous, dark grayish pink
Till, calcareous, sandy, dark yellowis h gray
Sand ; fine-grained gravel, dolomitic, gray
Sand and gravel, clayey, silty,
dolomitic, yellowish gray
Sand and gravel, dolomitic, yelllowish gray
Gravel t o
and a little sand;
dolomitic, gray
Till, calcareous, dark grayish pink
Till, calcareous, silty, yellowish
gra Y
Till, calcareous, gravelly, s i l t y ,
yellowish gray
Gravel and sand, clayey, silty,
gray
i"
Bedrock, dolomite
Driller's log of Austin well.
Sand, gravel, c l a y
Lime stone
2.
.
Stelter, Julius, farm, 1959, c e n , line N E ~ N fE s e c 28, T. 21 N., R. 8 W.,
Mason County. Elevation E .T .M 495 f e e t . Sample s e t 35414. Studied
by R. E Bergstrom
.
* Estimated
.
.
from t o p o g r a p h i c map.
27
Thickness
(ft1
Pleistocene Series
No samples
Wisconsinan Stage
Henry Formation
Sand, fine- t o medium-grained;
yellowish brown subanglular
grains ; ferruginous staining;
abundant yellowish quartz grains;
some brown silt
8.0
Sand, medium-grained, a s above;
some granular gravel
10.0
Silt, brown, calcareous
2.0
Sand, medium-grained; yellowi s h brown subangular grains
4.0
Sand, medium- t o coarse-grained
with granular gravel, yellowish
brown; granules of dolomite,
quartz, and granite
12.0
Sand, fine- t o coarse-grained, some
very c o a r s e grained, yellowish
brown; abundant grains of yellowi s h quartz and feldspar
12 .O
Kansan Stage
Banner Formation
Sankoty Sand Member
Sand, medium- t o coarse-grained,
pinkish gray; subangular t o
rounded grains ; abundant pink
and pink-stained quartz grains;
some granular gravel and finegrained sand beds
22.0
Sand, fine- t o very coarse grained,
pinkish gray; abundant pink
grains; some granules of dolomite,
quartz, feldspar, and igneous
rocks
10.0
Sand, fine- t o medium-grained,
reddish brown, subangular;
abundant pink grains; many
grains with pink c l a y skins
8.0
Sand, medium- t o very coarse
grained , pinkish gray; pink
grains; granules of chert, dolomite, and dark igneous rock
12.0
Gravel, granular, with very
coarse grained sand; granules
of dolomite, granite, sandstone,
f e l s i t e , and dark igneous rock
4.0
Depth t o b a s e
(ft1
98.0
106.0
118.0
122.0
(Total depth)"
* " T o t a l depth" I n d i c a t e s t h a t d r i l l i n g e i t h e r stopped i n unconsolidated rocks o r b a r e l y
penetrated bedrock.
Driller's log of Stelter well.
Thickness
(ft)
Top stratum
Fine-grained sand
Medium-grained sand
Mud
Medium-grained sand
Mud
Sand and gravel
Medium-grained sand
Medium-grained sand
Good sand and some gravel
Fine-grained sand
Medium-grained sand
Coarse-grained gravel and
some cobbles
Sand
Sand
Medium-grained sand and
some stones
Good gravel
Mostly sand, some gravel
Good sand and gravel
Depth t o b a s e
(ft
>
108.0
113.0
116.0
122.0
(Total depth)
3 . Held, Joe, No. 1 , 1954, S W ~ S E ~ SsW
ec~
. 8 , T . 1 0 N . , R. 4 W . , Montgomery
County. Elevation E T. M e 6 3 6 f e e t . Sample s e t 24625. Studied by
Elwood At herton.
.
Pleistocene Series
Illinoian Stage
Gla sford Formation
Till, noncalcareous , very silty,
light brown
Gravel, fine- t o medium-grained;
t i l l , calcareous, orange
Till, calcareous, brownish gray
Bedrock, s h a l e
Driller's log of Held well.
Surface s o i l
Clay
Shale and gravel
15.0
5.0
10.0
4 . Illinois Water Service Co. No. 38, 1950, 20 feet N. of c e n . of S. line
s e c . 36, T. 20 N . , R. 7 E., Champaign County. Elevation E.T .M 715
f e e t . Sample s e t 20601 Studied by J. W. Foster.
.
.
Thickness
(ft
Pleistocene Series
Wi sconsinan Stage
Wedron Formation
Soil, dark brown, and yellow,
clayey, noncalcareous t i l l
10.0
Till, yellow-buff, clayey,
calcareous
10.0
Till, gray-buff, s i l t y , calcareous;
some sand
20.0
Soil, black over yellow, noncalcareous till
10.0
Till, gray- buff, and scattered s o i l
(possibly c a v e d ) , calcareous
5.0
Till, pinkish, silty, calcareous,
and soil, a s above
5.0
Till, pinkish, silty, with sand
and gravel
15.0
Till, pinkish, s i l t y , sandy, with
scattered s o i l
5.0
Illinoian Stage
Gla sford Formation
Till, buff and weathered, noncalcareous, and black s o i l
5.0
Till, buff and yellow, partly calcareous; calcareous i n lower part 15.0
Till, a s above, very sandy
20.0
Till, a s above, with light brown
s o i l fragments
5.0
Till, yellow-buff, sandy, c a l careous; scattered black s o i l
10.0
Till, gray- buff, sandy and gravelly, pinkish i n lower part,
calcareous
55.0
Till, a s above, with strong
s o i l show
15.0
Kansan Stage
Banner Formation
Till, yellow, oxidized, noncalcareous, and black s o i l
5.0
Till, buff, sandy, gravelly,
calcareous
10.0
Mahomet Sand Member
Sand, yellow, very c o a r s e grained,
very dirty, with fine-grained
gravel i n lower part
35.0
Depth t o b a s e
(ft
Thickness
Depth t o b a s e
(fi)
(ft
Gravel, fine- t o medium-grained ,
very dirty, calcareous
10.0
Gravel, fine-grained, very
dirty, with s i l t interbedding
5.0
Gravel, fine- t o medium-grained,
dirty; scattered s o i l i n
lower part
15.0
Gravel, fine-grained , very
dirty; s o i l fragments
5.0
Gravel, medium-grained, dirty,
with till interbedding; calcareous 15.0
Gravel, fine- t o medium-grained ,
poorly sorted, dirty with t i l l
fragments and probable Pennsylvanian sandstone chips;
2.0
bedrock not detected
307.0
(Total depth)
e c .~ 8 , T . 1 7 N., R. 6 E . , Bureau
5 . Doty, S. L., 1935-1938, S E ~ S E ~ Ns W
County. Elevation E .T. M. 620 feet. Sample s e t 1619. Studied by
L. Horberg.
Pleistocene Series
Wisconsinan Stage
Henry Formation
Sand, medium-grained, slightly
calcareous, c l e a n , buff,
largely angular quartz
48.0
Kansan Stage
Banner Formation
Sankoty Sand Member
Sand, fine- t o coarse-grained ,
slightly silty; humus trace
4.0
Granular gravel; with some sand,
fine- t o medium-grained , polished 6 , 0
Sand, coarse-grained, gravelly,
calcareous; humus abundant
8.0
Silt, loe s s l i k e , calcareous,
yellow-gray; contains spores,
wood fragments
4.0
Sand, coarse- t o very coarse
grained, calcareous, numerous
polished and frosted grains
2.0
Silt, calcareous, l o e s s l i k e ; cont a i n s yellowish gray spores and
wood fragments
14.0
Sand, some gravel, medium- t o
coarse-grained, humus-stained 132.0
Bedrock, dolomite
Driller's log of Doty well
Thickness
(ft)
Depth t o base
(ft)
Sand, yellow
Sand and gravel
Sand, gravel, dirty
Silt and c l a y
Sand and gravel
Sand, medium-grained
Sand, granular, buff, red, black
Sand, buff, red, coarsegrained, polished
Sand, granular, buff, red, black
Gravel, buff, red, black, finet o medium-grained
Sand, scattered, granular
Gravel, sand
Dolomite
6. West BrooklynVillage No. 3 , 1948, S E ~ S W ~ Ms eNc . ~8 , T. 3 7 N.,
R. 1 E., Lee County. Elevation E .T .M 980 feet. Sample s e t 17800.
Studied by M. P. Meyer; modified by J. W. Foster.
.
Pleistocene Series
Wisconsinan Stage
Wedron Formation
Till, brown, grading t o sand
109.0
Sand, coarse-grained, and
clayey gravel
22.0
Sand, fine- t o mediumgrained, clayey
9.0
Till, brown, with gray
i n lower part
146.0
Illinoian Stage
Gla s ford Formation
Till, greenish, partly
noncalcareous
7.0
Till, gray, calcareous
28.0
Sand and gravel, s i l t y and
clayey, generally cleaner
near b a s e
105.0
Kansan Stage
Banner Formation
Humus on noncalcareous clay,
with sand and gravel i n
lower part
21.0
Till, gray, very sandy, gravelly,
calcareous
19.0
Sand, medium- t o very coarse
grained, slightly silty
18.0
Thickness
(ft)
T i l l , yellow and gray, noncalcareous, with thin sand
and gravel in lower part
Bedrock, sandstone
Driller' s log of We s t Brooklyn No
. 3 well
Top soil
Clay, yellow
Clay, brown
Clay and stones, red
Sand and clay
Clay, sand, and stones,
Sand and gravel, dirty
Sand, clay, and stones,
Clay and stones, red
Clay, red
Clay, sand, and stones,
Clay, sand, and stones,
Clay, sand, and stones,
hard
Clay, sand, and stones,
Stones, clay, and sand,
Sand, clay, and stones,
water-bearing
Sand, clay, and stones
Sand, clay, and stones
Sand, clay, and gravel
Sand, gravel, clay
Sand, clay, and stones
Clay, sand, and stones
Sand, clay, and stones
Sand and gravel
Sand, clay, and stones
Clay, brown, hard
Sand, dirty
Clay, sand, and stones
Sand, clay, and stones
Sand, dirty
Clay, hard
Sand and gravel
Sand rock, hard
red
red
red
blue
blue,
blue
hard
Depth t o base
(fi)
7. Northeastern Illinois Metropolitan Area Planning Commission Test Hole No. 1,
1962, S E ~ S E ~ Ss eW
c . ~7, T. 46 N . , R. 5 E . , McHenry County. Elevation
E.T.M. 975 feet. Core 4515. Logged by K. Swanson (Layne-Western Co.).
Thickness
(ft)
Pleistocene Series
Wisconsinan Stage
Wedron Formation
Clay, silty, gray, mottled
Till, yellowish red-brown t o gray
silty sand and sandy silt
Sand and gravel, gray; a few
silty layers
Sand, silty, gray-brown;
trace of c l a y
Silt, clayey, gray; a few
speckled seams of very
fine grained sand
Till, gray-brown clayey silt; a
few sand and s i l t seams
Silt, dark brown; trace of sand
and fine-grained gravel
Sand, brown-pink; a little grave l ; trace of s i l t and clay
Till, pink-brown sandy silt;
trace of gravel and clay
Sand, silty, dark gray; trace of
c l a y and gravel
Gravel, sandy, coarse-grained,
poorly sorted
Silt, gray-buff; small l e n s e s
of sand
Gravel, sandy, coarsegrained; trace of s i l t
Silt, brown; trace of clay
Gravel, gray-brown, some sand;
little c l a y and s i l t
Silt, hard, gray-brown; trace of
very fine grained sand
Till; medium-brown hard clay,
s i l t , sand
Bedrock, dolomite, gray-brown
Depth t o base
(ft)
473.5
(Total depth)
Counties i n Illinois
Illinois State Geological Survey Circular 490
35 p . , 5 f i g s . , 1 t a b l e , 1 app., 2 p l a t e s , 4000 c o p . , 1 9 7 5
Urbana, Illinois 6 180 1
Printed by Authority of State of Illinois, Ch. 1 2 7 , IRS, Par. 5 8 . 2 5 .