8 DRIFT DEPOSITS OF ILLINOIS. 



On a ravine a short distance south of Main street, the bluish 

 clay at the base of the above section is filled with fragments 

 and branches of wood, and a bone, thought by its finder to be 

 the femur of a human skeleton, was obtained from it, but un- 

 fortunately was allowed to crumble to fragments from a lack 

 of the knowledge required to preserve such fragile specimens 

 from destruction. 



The "loess" consists of buff and gray marly sand, and usually 

 caps the river bluffs, imparting to them the bald, knobby char- 

 acter so noticeable on the main water courses of the West. Its 

 maximum thickness in Illinois probably does not exceed sixty 

 to seventy feet, and is usually much less. 



At Quincy, the loess ranges in thickness from thirty to forty 

 feet, and is underlaid by a foot or more of chocolate colored 

 clay and a feAV feet of chert and brown clay, (local drift), 

 derived from the decomposition of the underlying Burlington 

 limestone. The chocolate colored clay contains twigs and other 

 vegetable remains, indicating that it was originally a surface 

 soil, and it is probably the equivalent of the "Forest-bed" of 

 the Ohio reports. 



The loess is not restricted to the vicinity of the rivers, but is 

 spread over wide areas in the central and southern portions of 

 Illinois. In the vicinity of Springfield it consists of two beds, 

 one of brown silicious clay, and the other gray marly sand, 

 aggregating a thickness of six to eight feet. 



In the western part of the county, and the adjacent portion 

 of Menard, these beds, frequently attain an aggregate thickness 

 of ten to fifteen feet, according to the statements of professional 

 well-diggers, and are usually underlaid by a black, mucky soil, 

 varying in thickness from two to three feet. 



The fossils of the loess comprise nearly all common species of 

 terrestrial, and a few species of fluviatile mollusca, and in addi- 

 tion to these it has afforded the largest portion of the fossil 

 mammalia hitherto found in this State. The Hon. Win. 

 McAdams, who has given especial attention to the fossils of 

 this horizon, has obtained a fine collection of mammalian re- 

 mains at Alton and Chester, embracing the bones of the Mas- 

 todon, Mammoth, Megalonyx, Bos primigenius, Castoroides 



