THE CLYDE SERIES OF SOILS. 



Indiana, all of Michigan, northern and northeastern Illinois, nearly 

 all of Wisconsin, and large areas in Minnesota and Iowa. 



The form of the ice lobes and the general direction of their ad- 

 vance seem to have been greatly influenced by the basins now occu- 

 pied by the Great Lakes. Thus, in the St. Lawrence Basin one of the 

 more eastern lobes was deflected by the Adirondack Mountain mass, 

 reaching its most southern limit at altitudes of 1,500 to 2,000 feet 

 above the present sea level where its southward spread was termi- 

 nated against the highlands of southern New York and northern 

 Pennsylvania. The extreme southwestern portion of this lobe ex- 

 tended to northeastern Ohio, where it terminated at elevations of 

 approximately 1,000 feet above sea level, occupying the rolling plain 

 which forms the northeastern extension of the Mississippi Valley. 

 Other lobes covered all of the southern peninsula of Michigan and 

 extended across the low plateau of northern Ohio and Indiana, of 

 northeastern Illinois and southeastern Wisconsin, terminating on the 

 low plain of the upper Mississippi Valley at altitudes varying from 

 TOO to 1,200 feet above sea level. 



In practically all instances this latest advance of the continental 

 glacier occupied territory which had previously been glaciated one 

 or more times. During the period of its advance and occupation 

 of this territory the Wisconsin glacier redistributed the unconsoli- 

 dated material which already existed within the region, filling many 

 of the deeper valleys which had been cut into the underlying rock. 

 It also brought fresh material from the Canadian Highlands and 

 from the more northern portions of the north-central States. In 

 addition it derived a considerable amount of material from the local 

 rock over which it passed. All of this material was deposited either 

 during the occupation of the region by the glacial ice or during the 

 slow northward recession of the ice sheet. 



The material thus deposited usually consisted of a heterogeneous 

 mass of coarse and fine particles derived from many diverse sources 

 and laid down either in the form of ridged moraines, where the ice 

 front was stationary for a considerable period of time; in the form 

 of gently rolling till plains, where the glacial material was deposited 

 beneath the ice in the form of ground moraine, or as stratified sand, 

 gravel, and bowlder deposits where streams of water flowed from the 

 iee front, or from caverns formed between the land surface and 

 the ice. 



As a result of these differences in the character of glacial action 

 the general land surface 'of the area occupied by the ice was first 

 smoothed by the glacial erosion of exposed surfaces, then further 

 leveled by the filling of protected depressions through the deposition 

 of glacial materials. Yet the final land surface maintained a consid- 

 erable degree of irregularity in surface elevation through a failure 



