THE MIAMI SEEIES OF SOILS. 9 



From this region the area occupied by the soils of the Miami series 

 extends westward in broad, undulating swells, the elevation varying 

 widely within the limits of a county, while smaller areas are usually 

 smooth or rolling. A general elevation of 900 to 1,000 feet is main- 

 tained to the western border of the region of Miami soils near the 

 Wisconsin River. Along the extreme western border some rough 

 and hilly country is encountered within the known limits of the oc- 

 currence of soils of this group. The most notable example of this 

 topography is found in the eastern end of the Baraboo ridge imme- 

 diately west of Portage, Wis. 



In general, the region occupied by the soils of the Miami series in 

 Wisconsin not only possesses greater variations in elevation than the 

 other sections dominated by these soils, but the local variations are 

 greater, the slopes are more pronounced, and the surface is rougher 

 and more complexly ridged than in the majority of the other regions. 



ORIGIN. 



All of the soils of the Miami series owe their origin to the glacia- 

 tion of the region in which they occur. 



Within recent geologic times practically all of the northern part 

 of the continent was repeatedly covered by glacial ice. The ice ad- 

 vanced as far south as the region of the Ohio River and as far west 

 as that of the Missouri. The successive advances and retreats of 

 the ice each occupied a considerable period of time and gave rise to 

 different deposits of materials which cover the central part of the 

 United States to depths ranging from a few feet to a maximum of 

 400 or 500 feet. 



The soils of the Miami series are developed chiefly within the 

 territory which was most recently covered by the ice. This inva- 

 sion is known as the Wisconsin stage of glaciation. 



During the Wisconsin stage of glaciation the center of dispersion 

 of the ice was undoubtedly within the region of the Canadian High- 

 lands to the northeast of the Great Lakes. From this section the ice 

 advanced as a thick sheet over all the territory to the south, ex- 

 tending as far as Chillicothe, Ohio, beyond Indianapolis, Ind., and 

 into eastern and northeastern Illinois. It occupied the greater part 

 of eastern and northern Wisconsin and covered considerable areas 

 west of the Mississippi River. 



In the region of the Great Lakes the ice sheet of the Wisconsin 

 glaciation characteristically occupied the chief lines and basins of 

 depression in the existing land surface in the form of broad tongues 

 or lobes, which have been given the names of the important lakes, 

 bays, and streams which now occupy these basins. 



55813°— Bull 142—14 2 



