( JZ GEOLOGY OF ILLINOIS. 



indicating the prevalence of dry land over a considerable portion of the pres- 

 ent area of the State, during the Post-tertiary period. Mr. John Wolf, of 

 Canton, reports a similar bed of black peaty soil, four feet in thickness, under- 

 lying the town of Fairview, at the depth of eleven feet. The heaviest deposits 

 of Drift occur along the Illinois river bluffs, and in the vicinity of Lewiston' 

 where the beds range from forty to sixty feet in thickness, while in the central 

 and western portions of the county, their general range is from thirty to forty 

 feet. 



The Loess caps the bluffs of the Illinois river, and extends back for three or 

 four miles, with a constantly diminishing thickness, towards the interior of the 

 county. This deposit consists of buff, or light brown, loamy sand, imperfectly 

 stratified, and locally contains an abundance of land and fresh water shells, 

 such as now accumulate at the bottom of fresh water ponds. Its presence in 

 the river bluffs is often indicated by bald, grassy knobs, which prevail more or 

 less wherever this formation is extensively developed. It is always uncon- 

 formable with the underlying deposits, and presents its greatest thickness 

 immediately at the river bluffs, thinning out rapidly towards the interior of the 

 adjacent region. Where it forms the sub-soil, and is overlaid by a loamy clay 

 soil, we find the heaviest growth of upland timber, such as sugar-maple, linden, 

 wild-cherry, black walnut and elm, and the lands, when reduced to cultivation, 

 are among the most productive in the State. This is the character of some of 

 the timbered lands in the vicinity of Lewiston, and at some other points in the 

 county adjacent to the river bluffs. When this formation was deposited, the 

 valley of the Illinois, as well as that of most of our large rivers, was a vast 

 fresh water lake, into which the sandy material that constitutes the greater part 

 of this formation was transported by the action of the rains, and streams of 

 running water that drained (he adjacent highlands. The fossils which it con- 

 tains, are mostly of the same species of land and fresh water shells that now 

 inhabit the adjacent region, but occasionally the remains of the Mammoth 

 Mastodon, Megalonyx, and some other extinct mammalia have been found in it 

 in this State. 



Older Geological Formations. 



The stratified rocks of this county belong, mainly, to the Coal Measures, with 

 a limited exposure of the St. Louis limestone in the valley of Spoon river. 

 Nearly all the uplands in the county are underlaid by coal, and we have found 

 here the most complete exposure of the productive Coal Measures that have 

 been met with in the State, and hence the section constructed in this county 

 will be considered a typical one, and will be used for the co-ordination of the 

 coal strata throughout the central and western portions of the State. We have 

 found here seven consecutive scams, all exposed by their natural outcrop, 



