GEOLOGY OF ILLINOIS. 



of wood. This was underlaid by seven or eight feet of hard blue clay. 

 This is the only place where a true soil under the drift clays was re- 

 ported to me in this county ; but it is quite probable the same thing 

 occurs at other points, the interesting fact being overlooked, or not con- 

 sidered worthy of especial attention by those who have had an oppor- 

 tunity of observing it. 



Good exposures of drift were met with along the bluffs of the small 

 creek west of Columbia, where it seems to be fifty feet or more in thick- 

 ness, and consists of buff or brown clay at the top, with bluish or pur- 

 ple beds at the bottom, the whole containing small pebbles of rnetamor- 

 phic rocks, and occasionally boulders of the same material of consid- 

 erable size, but rarely more than two feet in diameter. Where the ex- 

 posures occurred near the outcrop of the green and purple shales of the 

 Chester group the lower beds of drift seemed to approximate closely to 

 these shales in color, indicating the source from which they have, in 

 part at least, been derived. 



Stratified J? o c k $ . 



The paleozoic formations are largely represented in this county, inclu- 

 ding all the usual subdivisions of that age, from the lower Coal Mea- 

 sures to the middle of the Trenton limestone, except the Devonian and 

 Upper Silurian, which are wanting at the only locality where they should 

 appear, leaving a hiatus in the sequence of the strata, and allowing the 

 shales and shaly limestones of the Lower Carboniferous series to rest 

 directly upon Lower Silurian strata. 



There are two decided axes of disturbance in this county, the most 

 northerly of whicli intersects the Mississippi bluffs just over the line in 

 St. Clair county, and about three miles north-west of Columbia, and 

 extending thence about south 20 deg. east, passes a little to the east- 

 ward of that town, and to the westward of Waterloo, forming the high 

 ridge on which the old stage road runs between these points. The nu- 

 cleus of this axis is the Keokuk limestone, which may be seen well ex- 

 posed on a small creek intersecting this axis about half a mile east of 

 Columbia. There is about fifty feet of this limestone exposed here, the 

 upper forty feet consisting of coarse, thin bedded, brownish-gray and 

 cherty limestones, containing Spirifer Keo'knk, 8. neylectnx, and Arcliimc- 

 de* Owenana, while the lower ten feet of the exposure consists of blue 

 calcareo-argillaceous shales, with small geodes of quartz, the whole 

 probably representing the geodiferous beds of this group at more north- 

 ern localities. 



Immediately west of this outcrop the overlaying St. Louis limestone 

 dips west 20 deg. south at an angle varying from 20 to 30 degs., while 

 on the eastern side of the axis the dip in the opposite direction varies 



