TAZEWELL, Mo LEAN, LOGAN AND MASON COUNTIES. 179 



ness of the different beds. The quicksand, No. 8 of the above section, resem- 

 bles somewhat in appearance the sands of the Loess, and the only species of 

 the contained shells which could be identified was the Helicina occulta, which is 

 also not uncommon in the Loess of the river valleys in this State. Beds of 

 black vegetable mould are met with at less depths than in this section in vari- 

 ous places in this district, as for instance in the vicinity of Pekin, Tazewell 

 county, where it is said, in a few instances, to have tainted the wells which 

 penetrated to it to such an extent as to almost render the water 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, its thickness was found to be 

 ninety feet from the surface to the rock, at Lexington one hundred and eighty 

 feet, at Atlanta one hundred and twenty-six feet, at Lincoln seventy feet, at 

 Cheney's Grove one hundred and two feet, and at several points in Tazewell 

 county from sixty to one hundred feet or more. Its thickness is quite irregu- 

 lar, but seems, however, to be greatest in the central and eastern portions of 

 the district. In Mason county, we have no very reliable data upon which to 

 base our estimates, but its average thickness in that portion, I think, may be 

 safely put down at not less than fifty feet, and is probably much more. 



In the western part 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 irregu- 

 lar stratification, similar to that of beach deposits. A ledge of this material, 

 nine or ten feet in thickness, may be seen in the northwestern quarter of sec- 

 tion 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, and other similar ledges appear in various 

 places in the vicinity of Fond du Lac, and also on the Mackinaw, in the eastern 

 portion of the county. Another similar bed of cemented gravel, of, however, 

 a comparatively insignificant thickness, may be seen about half way up the face 

 of 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 portion of the district, either in Logan or McLean 

 counties, nor have I heard of its having been met with in sinking the various 

 shafts or borings. 



d oal Measures. All the stratified rocks which outcrop within the limits of 

 this district, belong, as has been already stated, to the Coal Measure-", and the 

 actual surface exposures are confined, for the most part, to a thickness of about 

 sixty or eighty feet of the middle portion of the formation. In the whole dis- 



