AFTONIAN INTERVAL 137 



definitely recognized. They were the first of these deposits to be assigned 

 to their true position in the Pleistocene column. In themselves these 

 gravels afforded little information concerning the time interval to which 

 they belong, farther than that the pre-Kansan ice had disappeared from 

 the region and that great floods, distributing the usual terrace materials, 

 poured along the drainage courses. In a paper on the Aftonian gravels, 

 in the Proceedings of the Davenport Academy of Sciences, volume X, it 

 was assumed that the floods carrying the materials of which the beds are 

 composed had their origin in the melting of the pre-Kansan ice, and that 

 these deposits represented simply the closing phase of the pre-Kansan 

 stage of glaciation. The assumption was based wholly on the ground 

 that it was difficult otherwise to account for streams of such volume and 

 persistency as would be required to transport and deposit the enormous 

 quantities of gravel found in Union county. Now, however, it seems that 

 investigations made by Shimek during the past four months may make 

 it necessary to modify the view expressed in the Davenport Academy 

 paper. Similar materials, quite as extensive as the beds at Afton Junc- 

 tion and Thayer, lying between the dark pre-Kansan below and typical 

 Kansan above (plate 2, figure 1), are found along the Boyer, the Soldier, 

 the Little Sioux, the Maple, and practically all the streams which drain 

 the western slope of Iowa. In these new localities the Aftonian gravels 

 have yielded the remains of a fauna representing river mollusks of mod- 

 ern species on the one hand and extinct terrestrial mammals on the other. 

 Both mollusks and mammals are found in such abundance, at such 

 widely scattered localities, and in such a state of preservation as to make 

 it certain that the fauna was contemporaneous with the deposition of the 

 gravels. They are not remains washed out of previous glacial or pre- 

 glacial formations. The mammals include forms which have been re- 

 ferred by some recent American writers to Elephas primigenius and 

 Elephas imperator; there is the common mastodon, Mammut ameri- 

 canum; there are two horses resembling the Equus complicatus and 

 Equus occidentalis of Leidy; a large stag related to Cervalces; an unde- 

 termined cavicorn ruminant and one or two other unidentified forms. 

 All the probisci deans are represented by teeth, and in addition to the 

 teeth there are the lower jaw of the large elephant, the left ramus and 

 symphysis of the mastodon, a perfect tibia, a nearly perfect humerus, a 

 femur nearly four feet in length, and yet lacking the proximal end; a 

 scapula which was perfect when taken from the pit, but was allowed to 

 go to pieces for lack of care; fragments of tusks up to four feet in 

 length, a few vertebrae, some pieces of the pelvis and unrecognized frag- 

 ments. There are a number of teeth from both horses, besides a large 



