THE WISCONSIN 65 



It has been indicated that coniferous plants during the Illinoian 

 glaciation must have been confined to a narrow strip paralleling and 

 adjacent to the ice margin. The same conditions must have obtained 

 during the Wisconsin. The lack of relics of this flora along the Shelby- 

 ville and Bloomington moraines is striking. From Edgar County, 

 Illinois, where the terminal moraine enters the state from Indiana, 

 west and north to La Salle County, almost no boreal relics occur. 

 The absence of pines may well be explained by the soil conditions, but 

 the swamps and bayous of the rivers are also without Larix and Thuja 

 and any of the ericads of the peat bogs of the north; even Caltha 

 palustris and Spathyema foetida are almost unknown along the glacial 

 boundary until well towards the northern end of the state, although 

 most of these plants are found freely along the moraine in similar 

 latitudes in Ohio and some in Indiana. At the north they reappear: 

 Abies balsamea, occurs in northeastern Iowa, and Pinus Strobas is 

 abundant from southwestern Wisconsin northward. Even Primula 

 Mistassinica occurs in northwestern Illinois. 



All of these facts of modern distribution may be explained by 

 postulating a glacial climate during the Wisconsin considerably drier 

 than at present and not much different in temperature, so that the 

 vegetation of extra-glacial Illinois assumed a xerophytic aspect. Under 

 this view, we may assume that the Ohio valley in southern Indiana 

 and Illinois was occupied by its present forest flora, possibly not so 

 luxuriantly developed; the Illinoian drift to the north of it by a 

 xerophytic forest of southeastern affinity with a slight admixture, 

 decreasing toward the west, of a prairie element; western Illinois 

 was exclusively prairie, of a type similar to that now prevailing pos- 

 sibly 400 miles farther west. A narrow and interrupted strip of 

 coniferous forest followed the glacial boundary, especially in places 

 where greater topographic relief afforded better shelter. Toward the 

 east, across Indiana and Ohio, the strip became broader and included 

 more species. Toward the north it broadened out again in the drift- 

 less area in the shelter of the deep rocky ravines, with the additional 

 protection of the projecting Des Moines lobe of ice extending south- 

 ward to the west of them. It is doubtful if any conifers or associated 

 species occurred west of this lobe. Tundra vegetation, less affected 

 by the environmental conditions, grew on the thin soil overlying the 

 ice back of the glacial margin. In general, the climatic conditions 

 and vegetation may have been shifted in this latitude 300 to 400 miles 

 cast of their present location. The presence of an old flora in the 

 Ozarks indicates that this shift did not extend much farther toward 

 the south. 



