THE EANSAN ICE INVASION 271 



to the Yarmouth interval. Three land shells are recorded from these deposits 

 near Freeport, Stephenson County. 



Succinea avara 

 Pupilla blandi 

 Pyramidula cronkhitei antlionyi 



These silts, which are very thick and vary in character (including a bed of 

 brown sand which may be an old soil), cover an extensive area in northwestern 

 Illinois. 



b. Loess 



An excellent exposure, showing two loesses, occurs in a ravine near the 

 line of Rock Island and Mercer counties. This section is reproduced below: 85 



Loess (post-Ulinoian) 25 feet 



Black soil (Sangamon) .■ 2-3 " 



Till, mainly of blue color (Tllinoian) 90 " 



Loess-like silt, very fossiliterous (post-Kansan) 12 " 



Height of section 130 " 



The following mollusks were obtained from the post-Kansan loess: 86 



Helicina occulta Slrobilops labyrinthica 



Helicodiscus paraltehts ( = lineatus) Succinea avara 

 Galba humilis modicella " luteola u 



Pyramidula perspectiva Zonitoides arboreal 



cronkhitei antlionyi (= slrialella) Polygyra species 

 Bifidaria armifera 



The mammoth, mastodon, and other vertebrated animals, no doubt, formed 

 a part of the fauna of the Yarmouth Interglacial Stage in Illinois. The mas- 

 todon is known from four localities. 

 Mammut americanum 



Henry County; Cambridge, in well 16 feet below the surface. 



Johnson County; Bloomfield, in yellow clay, 3 feet below the surface. 



Marion County; Sandoval, 12 feet below the surface. 



Washington County; Beaucoup, 18 feet below the surface, under the yellow 

 clay, in the older reddish clay. 



Old soil deposits, some of them containing wood, are known from the 

 following counties. These are apparently referable to the Yarmouth interval, 

 as they underlie Illinoian drift. 



85 Leverett, op. cil., p. 115. 



*" This is evidently the same list given by Udden in Proc. Iowa Acad. Sci., V, p. 103. 

 Polygyra species is the only added syjecies in Udden's list. The recent nomenclature is used. 

 Succinea luteola is a southern species, and the identification is probably an error for avara, 

 which is common in the loess. 



