WISCONSINAN MOLLUSCAN FAUNAS 23 



Molluscan faunas were recovered from loess, moraines, outwash, inclusions 

 of sand and silt within till, and from terrace deposits of Woodfordian age. Collect- 

 ing stations include 37 localities in the Peoria loess, two in the Morton loess, and 

 three in the Richland loess; two collections were made from silt-in-till inclusions 

 in the Normal and Metamora moraines, and six from Woodfordian terrace silts. 



The total Woodfordian faunal assemblage comprises 55 species, of which 

 22 species were not found at other stratigraphic levels. Predominant species in 

 the well defined assemblage include Columella alticola, Euconulus fulvus , Steno- 

 trema leal, Trlodopsis algonquinensls, and Vertigo modest a , all seemingly restricted 

 to the Woodfordian, and Angulspira alternata } Hendersonla occulta, Stenotrema 

 hirsutuw , Succinea ovalis, S. ielida , S. grosvenorl , Discus cronkhitei , and D. 

 macclintocki , each of which also occurs in other Wisconsinan assemblages. 



Woodfordian faunas display distinctive geographical differences from north 

 to south, but on the basis of present evidence it is not possible to make strati- 

 graphic distinctions within the substage. 



Interpretations of paleoecology may be generalized as follows: At least in 

 the region south of Sangamon River, Illinois was heavily forested in Altonian time; 

 these dense forests, existing in a climate more humid than the present one, con- 

 tinued through Farmdalian time and perhaps, in southern Illinois, into earliest Wood- 

 fordian. After Farmdalian time the vegetative cover was of a much more open type, 

 perhaps essentially a mixed prairie, with trees and shrubs restricted to borders of 

 stream courses and other favorable situations. 



There is no evidence of extremely rigid climates during Woodfordian time, 

 even in areas adjacent to ice fronts, although northern Illinois is judged to have 

 had a climate approximating that of the present Canadian Life Zone. 



REFERENCES 



Baker, F. C, 1920, The life of the Pleistocene or glacial period: Univ. Illinois 

 Bull. 17. 



Frye, J. C, and Leonard, A. B., 1952, Pleistocene geology of Kansas: Kansas 

 Geol. Survey Bull. 99, 230 p. 



Frye, J. C, and Willman, H. B., 1960, Classification of the Wisconsinan Stage 

 in the Lake Michigan glacial lobe: Illinois Geol. Survey Circ . 285, 16 p. 



Goodrich, Calvin, 1932, The Mollusca of Michigan: Univ. Michigan Michigan 

 handbook ser. mus. zool . no. 5, p. 1 - 120, figs. 1-7. 



de Heinzelin, J., 1959, Problemes du Pleistocene dans le Middle West (U . S. A.): 

 Soc. beige ge'ologie Bull., tome LXVII, p. 265 - 290. 



Leighton, M. M., 1948, Footnote on p. 390, in Washer, H. L., et al., Loess in 

 the southern Mississippi Valley — Identification and distribution of loess 

 sheets: Soil Sci. Soc. Amer. Proc . 1947, v. 12, p. 389 - 399. 



Smith, G. D., 1942, Illinois loess — variations in its properties and distribution: 

 a paleologic interpretation: Univ. Illinois Agr. Exp. Sta . Bull. 490, p. 

 139 - 184. 



Wayne, W. J., 1959, Stratigraphic distribution of Pleistocene land snails: Sterkiana, 

 no. 1, p. 9 - 18. 



