262 LIFE OF THE PLEISTOCENE 



Pisidium mediatium Planorbis antrosus 

 Valvala tricarinata " antrosus strialus 



" lewisii " deflectus 



Succinea avara " parvus 



Physa species (immature) " exacuous 



Galba palustris 



Two species, Segmentina armigera and Limnophysa (Galba) decidiosa 

 ( — obrussa) mentioned by Call, were not detected in the material examined. 

 Thirteen species are likewise included which were not mentioned by Call, 

 possibly because the material examined by him did not contain them. Valvala 

 sincera as identified by Call also proves to be V. lewisii. 



The fauna is seen to have been large and varied. The deposit was evi- 

 dently the bed of a large river or lake, and could not have been a tamarack 

 swamp, as stated by Todd, because mollusks such as Valvala tricarinata and 

 V. lewisii do not inhabit such a station. The tamarack log and cones mentioned 

 probably floated from the shore and became buried in the mud. That this 

 fauna lived in or near the present Andes Creek is very doubtful, because such 

 an assemblage of molluscan life would scarcely be found in this kind of an 

 environment. 



4. MINNESOTA 



Interglacial deposits referable to the Yarmouth interval occur in south- 

 eastern Minnesota between Kansan and Iowan tills. 55 * In Mower County 

 there is a bed of peat 6-8 feet thick beneath 50 feet of Iowan drift. 56 Pieces 

 of wood thot to be pine and cedar were found in the peat bed. Several other 

 sections in this vicinity as well as in other parts of the County, show this peat 

 bed to be widespread, to vary from 2 to 8 feet in thickness and to occur from 

 20 to 50 feet below the surface. 



Wood, apparently from the same horizon, occurs in Dodge, 57 Steele, 58 

 Waseca, 69 Goodhue, 60 and Dakota 61 counties. Records from Olmsted, Fil- 



" a Upham (The Sangamon Interglacial Stage in Minnesota and Westward) refers these 

 interglacial deposits to the Sangamon interval As the deposits underlie Iowan till and overlie 

 Kansan till, they may represent the entire interval between these two ice invasions. It is 

 probable that if these deposits could be carefully studied in the light of our present interpreta- 

 tion of Pleistocene phenomena, a break would be found in the deposits under consideration 

 representing the Illinoian ice invasion, if this part of the country was not glaciated at this time 

 The deposits in question seem as logically referable to the Yarmouth as to the Sangamon inter- 

 val. 



M Winchell, Geol. Minn., Final Report, I, page 363. 



" Op. cit., I, pp. 345, 375. 



•» Op. at., I, p. 402. 



"Op. cit., I, p. 413. 



M Op. cit., II, p. 51. 



" Op. cit., II, p. 98. 



