402 B. SHIMEK AFTOXIAX SANDS AND GRAVELS IN IOWA 



In these gravels were found numerous remains of extinct mammals 

 belonging to the genera EJephas, Mamut, Equus, etcetera, which are dis- 

 cussed more fully in Professor Calvin's paper. They were especially 

 abundant in the typical exposure shown in plate 33, and in the Peyton pit 

 at Pisgah. These remains consist of bones, teeth, and tusks, and are 

 more or less fragmentary and promiscuously distributed through the 

 coarser parts of the beds, having evidently been transported and scattered 

 by the same strong currents which moved the gravels. 



A vertebra of a small fish was also collected from finer gravel. A few 

 heavy-shelled TJnios were found, but they are more or less fragmentary, 

 the shells being chalky and very fragile. Only one species, QuadruJa 

 metanevra Eaf., could be positively identified. The species is now com- 

 mon in the rivers tributary to the Missouri. Unidentifiable fragments 

 of at least two other species are in the collection. 



The abundance and wide distribution of the bones and teeth in these 

 gravels and their comparatively good state of preservation suggest that 

 they were not derived from older formations or carried long distances, 

 but that the animals lived and died in comparatively close proximity to 

 the present burial ground of their remains. 



SANDS BEARING MOLLUSCAN FOSSILS 



The sand beds are stratified, and sometimes interbedded and cross- 

 bedded with finer gravel, and quite variable in fineness. They also vary 

 in color, some being rusty red with iron, others almost black with Mn0 2 , 

 and in the lower part of the deposit, beds of almost pure white sand often 

 occur. They usually contain small, very soft white calcareous nodules. 



The finer sand is sometimes cemented into plates and blocks which 

 usually grade into loose sand below. These blocks are sometimes so mas- 

 sive that they have the appearance of bedded rock, as in the exposure on 

 the east side of the Little Sioux river, near the north line of Harrison 

 county, and at Loveland and near Council Bluffs, in Pottawattamie 

 county, south of the Harrison county line. A little of this is shown 

 near the middle of the lower part of plate 37, figure 2. 



These finer sands contain numerous shells of fresh water and land 

 mollusks, all belonging to modern species, which are scattered through 

 the sand in much the same manner in which more recent shells are scat- 

 tered through the sand of modern river-bars. The shells are exceedingly 

 fragile and are difficult to handle, but a sufficiently perfect series was 

 collected to determine the identity of the forms with species now living 

 in the same region. The following species have been thus far identified : 



