716 



SCIENCE 



[N. S. Vol. XXXI. No. 801 



a swampy nature and contained numerous 

 summer-dry ponds, similar to those found in 

 the Skokie Marsh area. Above the peat de- 

 posit the surface soil is about two feet in 

 thickness. 



It has been stated by Goldthwait' and others' 

 that there are no certain traces of life in the 

 lake during the Glenwood and Calumet stages. 

 It may be true that life was not abundant 

 during the early part of the Glenwood stage, 

 but the evidence afforded by the deposits dis- 

 cussed above conclusively prove that life was 

 abundant during late Glenwood time, very 

 abundant during Calumet time and has con- 

 tinued to be so to the present time, for the 

 Chicago Eiver as well as the smaller streams 

 and summer-dry ponds in this area now teem 

 with molluscan life. 



The presence of a species of spruce (Picea 

 evanstoni) as well as an oak (Quercus mar- 

 ceyana) has led to the belief that a climate 

 similar to that of Alaska prevailed during the 

 early part of the period (Glenwood) during 

 which Lake Chicago was forming. The pres- 

 ence of Unio crassidens, essentially a southern 

 species, in the Calumet deposit, indicates, ap- 

 parently, a period of higher temperature dur- 

 ing this later time. That this species had a 

 much more northern distribution during early 

 postglacial time is evidenced by its presence 

 in a deposit at Green Bay, Wisconsin.' 



The northern records of crassidens may be 

 tabulated as follows: 



South of 

 Green Bay 

 Record 

 Wiaconsin, between Prairie du Chien 



and De Soto* 80 miles. 



Minnesota, not recorded. 



Iowa, Lansing" 80 miles. 



Michigan, not recorded. 



Illinois, Utica, La Salle Co.' 220 miles. 



Ohio, Scioto River' 260 miles. 



Indiana, Tippecanoe River^ 230 miles. 



'Bull. 111. Geol. Surv., No. 7, p. 63, 1908. 



= Alden, "Geol. Atlas of U. S.," Chicago Folio, 

 No. 81, p. 11, 1902. 



^Wagner, Nautilus, XVIII., pp. 97-100, 1905. 

 This specimen has been personally examined. 



*Chadwick, Bull. Wis. Wat. Hist. Soc, IV., p. 

 95, 1906. 



The most northern extension of this species 

 at the present time is in the Mississippi Eiver, 

 where it has been collected as far north as 

 Prairie du Chien and probably lives as far 

 north as De Soto. In Illinois and Indiana 

 the northern range is 150 miles farther south. 

 Crassidens is essentially a southern species, 

 abundant in the southeastern part of the 

 United States where its center of distribution 

 is in the neighborhood of Tennessee. Its 

 northern extension indicates a more genial 

 climate than that which now prevails in the 

 northern states. The route of migration to 

 Green Bay is difficult to predict with cer- 

 tainty. The Lake Chicago fauna undoubt- 

 edly migrated up the Mississippi-Illinois- 

 Besplaines Eivers. It is interesting to note 

 that the species associated with crassidens are 

 typical of a temperate climate and are, for the 

 most part, living in this region at the present 

 time. 



It is very important that records of crassi- 

 dens, both fossil and recent, be secured in 

 Wisconsin, Michigan and northern Illinois, 

 Indiana and Ohio. It is possible that the bed 

 of glacial Lake Maumee would reveal strata 

 similar to those observed in Lake Chicago, 

 and as crassidens is found in the Wabash 

 River, it may have migrated into Lake 

 Maumee. 



Studies on this subject are not now far 

 enough advanced to warrant generalizations. 

 A report illustrated by photographs and strati- 

 graphical sections, and with tables of the spe- 

 cies, together with their geographic distribu- 

 tion, past and present, is in preparation. The 

 writer would solicit authentic northern records 

 of crassidens for the purpose of establishing 

 the present geographic distribution of this 

 species. It would also be of great value if 

 crassidens could be discovered in postglacial 

 deposits in Wisconsin and Michigan, as well 

 as in northern Ohio and Indiana. FuU credit 



^ Museum record. 



« Baker, Bull. 111. State Lab. N. H., VII., p. 77, 

 1906. 



' Sterki, Proo. Ohio Acad. Sd., IV., p. 392, 1907. 



' Daniels, 27th An. Rep. Dept. Geol. Ind., p. 650, 

 1902. 



