DRIFT DEPOSITS OF ILLINOIS. 23 



gence of the surface, and the accumulation of the sands, clays, 

 etc., that underlie the soil which occurs immediately beneath 

 the boulder clays. 



Then the surface was elevated and the marshy swamp soil 

 under these clays was formed. A second submergence then fol- 

 lowed and through the agencies of water currents and ice-floes, 

 the boulder clays were deposited. 



This was followed by a partial elevation of the surface and 

 the prevalence of lacustrine conditions, resulting in the deposit 

 jof the loess, while the adjacent dry land was inhabited by now 

 extinct forms of mammalia, associated with some of those still 

 existing in the same region. This was followed by the final 

 emergence of the whole area, and the commencement of the ex- 

 isting order of things. 



The mammoth and mastodon were certainly coeval with spe- 

 cies of mammalia still existing in the Mississippi valley. This 

 fact has been clearly established by the collection of fossils made 

 by Mr. Me A dams from the loess, and by the fossil bones found 

 between Illiopolis and Niantic, near the east line of Sangamon 

 county. At this locality beneath a black mucky surface soil 

 only four feet in depth, the remains of a mastodon consisting 

 of the jaws with the teeth intact, both tusks, and several of the 

 large bones were found associated with bones of the buffalo, 

 elk and deer, all embedded together in a bed of quicksand that 

 had probably once formed the bottom of a pool of water to 

 which these animals resorted, and in which they perished. The 

 writer was present during the disinterment of these remains, 

 and some of the small bones of the mastodon and all those of 

 the smaller animals except the antlers of the elk are now pre- 

 served in the cases of the State Museum of Natural History. 



No well authenticated discovery of the remains of mammalia 

 in this State in beds older than the loess or modified drift, has 

 come to the knowledge of the writer, and in every case where 

 such finds have been reported, investigation has shown that 

 they were obtained from beds more recent than the boulder 

 clays. Isolated bones and teeth are often obtained from the 

 alluvial banks of the streams, but more frequently they occur 

 in the black peaty soil or subsoil of the marshes, in which they 

 seem to be better preserved than when buried elsewhere. 



