274 GEOLOGY OF ILLINOIS. 



creek, where it is crossed by the road from Waterloo to Belleville, 

 partial outcrops of the lower Chester limestone, and the overlaying 

 shales, are seen on a branch of the creek, and on the main stream the 

 second bed of limestone and the overlaying shales are well exposed, 

 and are filled with the characteristic fossils ot this group. 



Three miles south of Freedom, at the crossing of Prairie du Long 

 creek, the entire bluff is composed of Chester limestone and shales. 

 This exposure is about fifty feet in thickness, consisting of coarse, 

 granular and partly crinoidal limestones, with intercalated bands of 

 shale, containing many of the characteristic fossils of this group. We 

 obtained at this locality the following species in addition to those men- 

 tioned on a previous page, from about the same horizon : PentremitcH 

 sulcatus, Zeacrinus maniformis and Z. Wortheni. The best exposures of 

 these limestones in this county may probably be found on this creek 

 and its tributaries, and the entire thickness of the group in the south- 

 eastern part of the county cannot be less than 250 feet. 



These limestones and shales are also partially exposed on tLe western 

 borders of the synclinal basin already referred to, but the exposures 

 are mostly isolated, and no continuous section of the several divisions 

 of the group can be seen, but fine localities for collecting the fossils ot 

 this horizon occur in this part of the county. 



St. Louis Limestone. This limestone occurs in extensive outcrops in 

 the county, and in two well marked divisions. The upper division 

 consists mainly of light-gray, compact, regularly uedded limestones, 

 with some thin, shaly partings ; and the lower, of buff or brown marly 

 and partly magnesian beds, with some very massive layers ot a semi- 

 oolitic, nearly white limestone, which are well exposed about a mile 

 east of Columbia, where they constitute the upper beds of this division. 

 This group forms the main portion of the river bluffs from the center of 

 township 1 south, range 10 west, to Eagle Cliff, below which the Keo- 

 kuk and Burlington beds gradually rise above the surface, and cap the 

 the hills in the vicinity of Salt Lick Point, near the south line of town- 

 ship 2 south, range 11 west. Below this point these limestones soon 

 dip again below the surface, and the St. Louis group, with an occa- 

 sional outcrop of the Keokuk beds, continue to form the main portion 

 of the river bluffs to the south line of the county. 



The upper division of this group forms the bed rock over a consider- 

 able portion of the county, and wherever this is the case the surface is 

 covered with sink holes which form a sure guide to the extent of i f s 

 outcrop. All of that portion of the county lying between Fountain 

 creek, west of Waterloo, and the river bluffs, and extending thence in 

 a belt from three to six miles in breadth, in a south-easterly direction, 

 to the Kandolph county line, is covered with sink holes, and for agri- 



