344 S. CALVIN AFTONIAN MAMMALIAN FAUNA 



ing of fossil remains at this point, but the outcrop is of especial interest 

 for the reason that the overlying Kansan and the underlying pre-Kansan 

 drift sheets are both exposed in place, with the weathered' and f erruginous 

 Aftonian between them. At Pisgah and Missouri Valley the till below 

 the Aftonian beds is not in sight. 



Farther up the valley of the Little Sioux, at Turin, in Monona county, 

 some good fossil remains have been found, and there are pits near Cas- 

 tanea and Mapleton, in the Maple valley, which have produced bones of 

 Aftonian mammals. 



A very promising area, which has not yet been carefully investigated, 

 embraces a number of sections in the southeast corner of Lyons township, 

 Mills count}'-, and the adjacent sections in the northeast part of Scott 

 township, Fremont county. The Aftonian gravels occur in natural ex- 

 posures within this area at a number of points, and they have been pene- 

 trated in farm wells which have gone down through the Kansan drift. 

 There are trustworthy reports that mammalian bones have been taken 

 from the gravels in some of the wells, and a number of finds have been 

 made in the gravel pits, which are operated here on a relatively small 

 scale. A complete set of left molars of a large horse, upper and lower, 

 was found by Mr E. L. Gladwin while grading a road in section 35, 

 Lyons township, Mills county, and is now in possession of the writer. A 

 considerable portion of the skeleton was present, but the bones were too 

 soft for preservation. Both upper and lower series of this fine set is 

 illustrated in plate 17. The Gladwin horse was found in a fine blue clay, 

 a bed of silt, that here in places overlies the gravels but is of the same 

 age. Similar silts occur with the gravels, but interbedded with them, at 

 Missouri Valley and Pisgah, in Harrison county. 



The Aftonian Horses 



In the collections under consideration horses are represented by a 

 much larger number of bones and teeth than any of the other types of 

 Aftonian mammals. There are bones from nearly all parts of the skele- 

 ton, but leg bones and foot bones are most common and most significant. 

 Among the teeth there are eighteen superior molars and premolars and 

 about an equal number from the lower series. The Gladwin set is the 

 only one that is complete; the other teeth show great variations in the 

 amount of wear and in minor details, and it is quite certain that they 

 represent a number of individuals. At least two species seem to be 

 clearly indicated. In one the teeth are larger than those of the modern 

 species, as is shown by the following comparisons and measurements of 

 the upper molars of the Gladwin horse. Comparison is made with the 



