THE MIAMI SEEIES OF SOILS. 11 



accomplished beneath the ice and in the lower zones of the glacier. 

 At the same time other materials, frequently derived from remote 

 sources, were carried within the upper part of the glacier and upon 

 its surface. 



The glacial advance to the extreme limits of the Wisconsin stage 

 of glaciation occupied a long period of time. There is also evidence 

 that the ice front remained stationary, or nearly so, along the region 

 of its extreme advance for some time, resulting in the thickening of 

 the ice-deposited material along the outer margin of the glaciated 

 region, forming hills and ridges of some elevation. These deposits 

 are technically known as moraines, and comprise the material car- 

 ried under, within, and upon the ice and piled up as a heterogeneous 

 mass of stone, gravel, sand, and clay where the ice was melting along 

 a nearly stationary position at its terminus. The outer margin of 

 the area covered by the Wisconsin stage of glaciation is quite com- 

 monly marked by such morainal accumulations. Sometimes these 

 moraines are heaped against more elevated land, which arrested the 

 advance of the ice. Such moraines occur along the southeastern bor- 

 der of the area under discussion, particularly from near Chillicothe, 

 Ohio, to the vicinity of Lancaster, Ohio. In other locations the front 

 of the ice rested upon a nearly flat surface, and the morainal front 

 rises from the outer plain like a low, irregular wall. The southern 

 border of the region occupied by the soils of the Miami series is 

 chiefly of this character from Chillicothe westward to the Wabash 

 Eiver and throughout a great part of the southwestern and western 

 margin of this stage of glaciation. 



From this position of its extreme advance the ice slowly receded, 

 with numerous periods of halting and some stages of readvance over 

 territory which had been once freed from its ice cover. At each of 

 the stages of halting large or small marginal moraines were formed 

 which still exist as low, rolling ridges, usually occupying long, nar- 

 row belts of higher land arranged concentrically with the margin of 

 the individual ice lobes and around the extremities of the basins 

 through which the various ice sheets advanced and retreated. 



Between these swelling and rounded moraines the material which 

 was carried under and within the ice sheet was distributed in the 

 form of a thick sheet of clay, sand, gravel, and bowlders known as 

 glacial till. A cut in this material is shown in Plate I, figure 2. This 

 material does not differ greatly from that of the thicker morainal 

 accumulations, except in having a more nearly level surface and in 

 the lack of linear ridging and hummocky surface features. In gen- 

 eral there are more extensive areas of water-washed and stratified 

 material at some points within the moraine areas than within the till 

 plains, although the work of the water from the melting ice is rec- 

 ognized to some extent in each of these forms of glacial deposition. 



