THE KANSAN ICE INVASION 261 



In Douglas County the Yarmouth is apparently represented beneath the 

 Wisconsin till, the deposit being seen in well sections. One such, two or three 

 miles north of Grandview (S. E. quarter section 33, T. 100, R. 64) contained 

 wood, cones, shells, etc. in muck, and was situated 20 feet below the surface. 

 Todd thus refers to this material. 54 "An ancient tamarack swamp. — Near 

 Grandview, in the southeast quarter of sec. 33, T. 100, R. 64, were found traces 

 of more recent occupation of the region by trees. In a well which had been dug 

 on the edge of a basin near a branch of Andes Creek, at the depth of 20 feet 

 was found a layer of muck several inches in thickness, in which were pieces 

 of wood with numerous fresh-water shells of nearly a dozen species. But the 

 most remarkable thing was the stem of a hemlock or tamarack about 10 inches 

 in diameter lying across the well, and in the muck were numerous cones, evi- 

 dently of the same species. Overlying this trace of a tamarack swamp was 

 mud of various colors and consistency, evidently washed from the surrounding 

 hillsides. That it should be so deeply buried was chiefly explained by its 

 connection with the channel of Andes Creek. This was conclusive evidence 

 that the region had been occupied more or less by timber since the ice had 

 covered the region, possibly while the second moraine was in process of forma- 

 tion. Similar finds are reported from wells several miles west of that place. " 



The overlying till here is Wisconsin, which varies greatly in thickness. 

 The surface is yellow clay, underlaid by blue clay. The former is Wisconsin, 

 while the latter is apparently Kansan. Prof. Todd evidently correlates the 

 deposit with the later Wisconsin when he says " this was conclusive evidence 

 that the region had been occupied more or less by timber since the ice had 

 covered the region, probably while the second moraine was in process of forma- 

 tion. " The indications are that the underlying blue clay was laid down 

 by the Kansan ice sheet, and hence the fossil remains must be regarded as 

 post-Kansan and pre- Wisconsin. 



From this new angle of view the fossils become of great interest. The 

 mollusks were submitted by Prof. Todd to Prof. R. Ellsworth Call, who 

 recognized the following species r 55 



Limnophysa palustris Vahata sincera 



decidiosa Segmentina armigera 



Gyraulus parvus 



Recently, the material gathered by Prof. Todd was submitted to the writer 

 for study by Mr. W. H. Over, of the University of South Dakota museum, and 

 fifteen species were recognized, as noted below: 



Pisidium compressum Lymnaea slagnalis appressa 



variable Planorbis trivolvis 



" Todd, Bull. 158, U. S. Geol. Surv., p. 121. 



K Op. cil., p. 121, footnote. The old nomenclature is used. 



