THE NEBRASKAN ICE INVASION 237 



till in some places. The section in the cutting of the Illinois Central Railway, 

 as interpreted by Shimek, is shown below. 



Sandy, somewhat loess-like stratum, possibly aeolian 2-5 feet. 



Gray, weathered drift, probably Kansan *. 7-9 feet. 



Gravel, sand, and silt: 



Sand, gravel, and boulders 1-2 feet. 



Silt, with sand and pebbles, ferruginous 2-A feet. 



Sand, gravel, and boulders 5-6 feet. 



Weathered gray drift, probably Kansan, exposed 2 feet. 



From the silt a number of mollusks were obtained together with the bones 

 of a horse. 73 



* Planorbis bicarinatus (=antrosus) Galba reflexa 



* " -parvus * " caperata 



" dilatatus " humilis modicetta 



Ancylus rivularis * Pisidium compressum 

 Vakata tricarinala " abditum (?) 



Amnicola species Sphaerium sulcatum (=simile) 



Segment ina armigera Anodonta imbecilis (?) 



* Physa Integra * Vallonia costata 



" sayi(?) Eqims scotti (E. laurentius, vide Hay) 



In the Collins sand pit the following evidences of life were observed: 79 



Unio species Equus scotti (E. niobrarensis, vide Hay) 



Sphaerium sulcatum (=simile) Castoroides species 



Mastodon and musk ox bones are recorded by Todd from lower strata east 

 of Sioux Falls, near the Big Sioux River. 80 



6. Montana 



Alden 80a records a pre-Wisconsin glacial drift in the region of Glacier 

 National Park which is thot possibly to correspond with the Nebraskan or 

 Kansan drift sheets. A second pre-Wisconsin is also thot possibly to be repre- 

 sented. A section on St. Mary River north of Sloan's Ranch, just north of 

 the International Boundary, exhibits the following strata: 



Northeastern till, containing crystalline boulders 



Loess, sandy at top 6 feet 



Soil, black clayey loam, consisting of the weathered surface of the lower loess bed 10 feet 



Typical loess, containing concretions, hard shells, and bones of small animals 5 feet 



Northeastern drift containing many decomposed boulders 2 feet 



Shale 



" Those species marked with an * were included in Todds list, where, however, Physa 

 Integra is identified as Physa heterostropha. 



79 Calvin, Bull. Geol. Soc. Amer., XXII, pp. 211-212. 



80 Bull. No. 158, U. S. Geol. Surv., p. 85. 



,,a Bull. Geol. Soc. Amer., XXIV, p. 546, 1913. 



