236 GEOLOGY OF ILLINOIS. 



the terrace epoch, when the waters in the valley of the Illinois stood at a 

 level of fifty feet or more above the highest point attained by the waters 

 of the existing- streams, but still subsequent to the accumulations of modi- 

 fied drift that forms the main portion of the bluff at Peoriu, and along the 

 north bank of the Kickapoo for some distance beyond Edwards station. 

 These sandy terraces occurring at about the same level, are a charac- 

 teristic feature of the Illinois river valley, and most of the towns from 

 Naples to Peru are built upon them. We were not able to obtain any 

 reliable section of the beds constituting this terrace, but so far as could 

 be seen from partial exposures of the strata on the small streams that 

 cut through it, the upper portion at least is composed mainly of sand 

 and gravel. 



The modified drift deposits, which form the main portion of the bluff 

 at Peoria, are about seventy-fiA T e or eighty feet in thickness; and for 

 the following section, made in sinking a well from the top of the bluff 

 in that city, I am indebted to my friend E. G. Johnson, esq. The well 

 was four feet in diameter, and was carried down ninety-seven feet, and 

 then a boring was made eight feet more. The section is as follows : 



No. 1. Urowii prairie clay and soil 12 feet. 



No. 2. Coarse gravel and sand, with boulders 35 " 



No. 2. Clay and sand, forming seven or eight distinct beds, some containing coarse gravel and 



boulders 48 ' 



No. 4. Black, mucky soil, with limbs of trees, etc 2 " 



No. 5. Boulder clay 8 ' 



Nos. 2 and three constitute the modified drift deposits of this section, 

 and their aggregate thickness is eighty-three feet. Mr. Johnson re- 

 marks, in his letter transmitting this section to me, that "at the depth 

 of about eighty feet from the surface we found a considerable heap of 

 charcoal : evidently such as would be left by a fire made of branches of 

 trees from a half inch to an inch in diameter ; a small fire, big enough 

 to have boiled a kettle or cooked a venison steak." This proves con- 

 clusively the existence of man in this region anterior to the epoch of 

 the modified drift, and we may reasonably expect that evidence will 

 yet be found to prove his existence here anterior to the deposit of the 

 boulder clay. No. 2 of the foregoing section contains boulders of all 

 the varieties of metamorphic rocks usually occurring in our drift de- 

 posits, and of all sizes up to a diameter of three or four feet. The full 

 extent of this deposit inland from the river bluffs we were unable to de- 

 termine, but it extends westward to the valley of the Kickapoo, and 

 northwardly it is exposed on all the branches intersecting the bluffs for 

 several miles. The ancient valley now T in part occupied by the Illinois 

 river was apparently at one time fully twice its present width from the 

 outlet of the Snatchwiue to the Kickapoo, and its western portion has 

 been subsequently filled with these drift accumulations. In the north- 



