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[The Geology of Mason county being reported by the above author in connection with Tazewell, McLean and Logan, we are compelled to give data from those counties; also from Menard and Cass, from the fact that the geological formations of these six counties are so uniformly the same that a description of one is nearly a description of all. It is also true that the geological surveys of these six counties have been very superficial and neglected. Our State Gealogist, Prof. A. H. Worthen, being only remarkable for giving little attention to the important work which the State employs him to do. We shall extract from the work of Mr. Bannister, done for the Geological office of this State, and add such personal investigations as we have been able to make.]

“ The surface of the country over a great portion of the district composed of the counties of McLean, Logan, the greater part of Tazewell, and the eastern part of Mason, is a high, undulating prairie, with here and there groves and belts of timber.

The soil is generally a rich brown mould, varying somewhat in different localities in the proportions of clay, etc., which it contains, some portions being more argillaceous than others. In the timber, however, which occupies scarcely more than one-fifth or one-sixth of the entire surface, and the broken country along some of the principal streams, the soil is somewhat of a different character, the lighter colored and more argillaceous subsoil appearing at or near the surface.

In the greater part of Mason county, and over considerable tracts in the southwestern part of Tazewell county, the surface configuration varies from that which we have described. The

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prairies are low and comparatively flat, and in many places were originally overflowed, or marshy, at some seasons of the year. The soil of these prairies is a rich alluvium, generally more or less arenaceous, which forms, when sufficiently elevated or drained, one of the best producing soils in the State.

Along the Illinois and Sangamon rivers, in this region, we find rather extensive sandy tracts of river formation, and on the Sangamon river in Mason county, and on the Illinois in Mason and Tazewell, the bold bluffs of the Loess are, in some localities, conspicious features of the general landscape.

The principal streams occurring in this district, besides the Illinois and Sangamon rivers, which form a portion of its borders, are the Mackinaw, in Tazewell, Mason and McLean counties; Salt Creek, in Mason and Logan counties; Kickapoo and Sugar creeks, in Logan and McLean counties. These, with many minor streams and nameless tributaries, drain nearly the whole surface of this whole district. With the exception of the Illinois and Sangamon rivers, none of the streams have extensive tracts of bottoms adjoining them, and even along these rivers the bottoms are either of inconsiderable extent or wanting altogether.

The geological formations appearing in this district are almost entirely of the drift or later formations, the older rocks outcropping only at a comparatively few localities in Tazewell and Logan counties. The underlying rock, as far as can be ascertained from these outcroppings, as well as from artificial exposures, by shafts, etc., in various parts of the district, consists entirely of the different beds of the coal measure series.

The Loess, the uppermost of the more recent geological formations, appears only in the vicinity of the Illinois and Sangamon rivers, and consists here, as elsewhere, of buff or ash colored marly sand, containing fresh water shells of existing species. It is not everywhere equally well developed, and in various localities along the Illinois river, in Mason and Tazewell counties, it either does not appear at all, or is inconspicuous. It may be well seen, however, in Mason county, where it appears in the bald, rounded bluffs, with occasional mural-appearing escarpments covering their summits, which forms so characteristic a feature of the landscape along the river below. In the northern part of Tazewell county, although this bluff marl sand appears to some extent in the bluffs along the Illinois river, it is not by any means as well exposed or prominent as farther south, in other counties.


The drift formation which covers the older rocks in almost every part of this district, is here composed of beds of blue and brown clay, sand and gravel, and varies in thickness in different portions from fifty feet in the western part of Tazewell county, to two hundred and fifty in the Bloomington shafts. It has been penetrated however at but comparatively few points, and over the greater part of this region, its depth can only be approximately estimated. It seems probable indeed that it may be of this thickness over a considerable portion of McLean county, as boring at Chatsworth in the adjoining portion of Livingston county, was reported to have penetrated to a depth of two hundred and fifty feet before striking rock. The material of the drift in this region appears to be roughly stratified; alternating beds of sand, gravel and clay are frequently met with in wells and borings. The sand and gravel beds make generally but a small part of the total thickness, though sometimes single beds attain a very considerable thickness, as, for instance, at Chenoa, in the northern part of McLean county, where a boring for coal passes through a bed of sand and gravel thirty feet in thickness, overlaid by forty-five feet of the usual clays of this formation, Occasionally also a bed of black earth or vegetable mould, still containing pieces of wood, trunks of trees, leaves, &c., only partially decayed, is met with, and a bed of quicksand containing the usual fossil land or fresh-water shells of existing species.

The following section of the drift afforded by a shaft sunk in the city of Bloomington, is of special interest, as showing both of these conditions at unusual depths. The shaft was sunk by the Bloomington Coal Mining Company near the track of the Chicago and St. Louis Railroad, half a mile north of the depot: 1 Surface soil and brown clay...,

10 feet. 2 Blue clay. ..

40 3 Gravelly hardpan....

60 4 Black mould with pieces of wood..

13 5 Hardpan and clay..

89 6 Black mould, &c....

6 7 Blue clay...

8 Quicksand, buff and drab color, containing fos-

sil shells...
9 Clay shales (coal measures)...


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Another shaft a little over a mile distant from this one passed through materially the same succession of strata, with only local variations in the thickness of the different beds. The quicksand, No. 8 of the above section, resembling the sands of the Loess in general appearance, and the only species of the contained shells which could be identified, was Helicina Occulta, which is also not uncommon in the Loess of the river valleys of this State. Beds of black vegetable mould are met with at less depths than in this section in various places in this district, as, for instance, in the vicinity of Pekin, Tazewell county, where it is said in few instances to have tainted the wells which have penetrated it to such an extent as to almost render them unfit for use. Sections of the drift are also afforded by the borings for coal which have been made in various parts of this district. In all cases they show variations of the material from blue to yellow clay, sand and gravel, but do not generally afford sections of such especial interest as the shafts at Bloomington, nor is the depth of the formation as great. At Chenoa the thickness is found to be ninety feet from the surface to the rock; at Lexington one hundred and eighty feet; at Atlanta one hundred and twentysix feet; at Lincoln seventy feet; at Cheney's Grove one hundred and twenty-two feet; and at several points in Tazewell county from sixty to one hundred feet and more. Its thickness is quite irregular, but seems to be greatest in the central and eastern portions of the district.

In Mason county we have no reliable data on which to base our estimates, but its average thickness in that portion I think may be set down at not less than fifty feet, and is probably much more. In the western portion of Tazewell county in the ravines and broken country along the Illinois river, I observed in a number of places at the base of the drift a bed of cemented gravel or conglomerate showing sometimes an irregular stratification similar to that of beach deposits.

A ledge of this material may be seen, nine or ten feet in thickness, in the northwestern quarter of section 7, township 25, range 4, west of the third principal meridian, up one of the side ravines which comes down through the Illinois river bluffs a little south of Wesley city, in Tazewell county, Illinois, and other similar ledges appear in various places in the vicinity of Fon du Lac, and also on the Mackinaw, in the eastern portion of this county. Another similar bed of cemented gravel, of, however, a comparatively in

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significent thickness, may be seen about half way up the bluff, at the steamboat landing in the city of Pekin, where it does not appear to be more than a few inches thick.

I have not observed any similar deposits in the eastern portions of this district, either in Logan or McLean counties, nor have I heard of its having been met with in sinking the various shafts or borings.


All the stratified rocks that outcrop within the limits of this district belong, as has been already stated, to the coal measures, and the actual surface exposures are confined for the most part to a thickness of sixty or eighty feet in the middle portion of the formation. In the whole district there is but one boring which affords an artificial section of the beds down to the base of this formation. This is one made by Voris & Co., on the bottom lands on the Tazewell county side of the Illinois river, and directly opposite the city of Peoria.

The first bed of the coal measure which is met with in the boring is about forty feet below the lower coal seam, which is worked in this section, number four of the Illinois river section, as given by Prof. Worthen.

The following is a section of the first four hundred and fiftynine feet of the boring. Below that depth the records kept by Mr. Voris & Co. are not complete, as to the thickness and material of all the different beds

I Alluvial soil of river bottom..
2 Sand.......

3 Gravel (boulder drift).
4 Clay shale

5 Bituminous slate.....

3 6 Fire clay....

15 7 Clay shale..


4 feet

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I 20

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8 Coal.....
9 Clay shale....
10 Sandy or argillaceous shale (very hard)....
II Sandstone...
12 Nodular, argillaceous, limestone..

4 34 34 4 6



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