175 



Two fli.stinct periods of glaciation are recognized and in addition 

 mncli material derived from a third, in \vlii(,-h the advance of the ice 

 sheet did not reach the limits of Indiana, but produced many important 

 features by the action of wind and water upon the outwash material. 



The various stages producing glacial deposits are spoken of as ( 1 ) 

 The First Ice Invasion, chietly that of the Illinoian ice sheet and probably 

 an eastern lobe which reached the eastern side of Indiana. (2) The Main 

 Loess Depositing Stage, the lowan drift. (3) The Wisconsin Stage of 

 Glaciation. 



First Ice I)ivasion. — The State was invaded by ice which had its cen- 

 ter of dispersion in the elevated districts to the east and south of Hudson 

 Bay. From the region to the north of Lake Huron there was a move- 

 ment to the west of south over the Lake Michigan Basin, Illinois and 

 western Indiana. From a part of this sheet the part known as the Illi- 

 noian lobe was formed. The deposit left by this invasion constitutes the 

 surface (aside from the thin covering of loess) over southwestern 

 Indiana and an area of almost equal size in southeastern part — 

 that is, It covers the entire area bet\A'een the glacial boundary and the 

 line of the Wisconsin drift. Many wells and drillings have shown that this 

 drift is also present farther to the nortli underlying the Wisconsin. The 

 thickness of this drift over the area of its exposure is in general about 

 twenty-five feet except in filled valleys. In places the ridges carry but a 

 thin coating, while adjoining valleys may be filled lOO feet or more. At 

 the southern limit the coating of material is very thin in most places, and 

 while the boundary is not marked by a w^ell defined ridge, the character 

 of the soil and the natural vegetation mark approximately the limits of 

 the drift. 



In general, the material is of a yellowish brown color to a depth of 

 fifteen feet or more, beneath w'hich the color is a gray or blue gray. There 

 is every transition from the brown to the gray; it is therefore probable 

 that the brow'U is an altered gray till, the oxidation of the iron having pro- 

 duced the color. In the filled valleys sand and gravel are often found, and 

 in Ihc northern part of the area the drift becomes more variable. The 

 underlying rock formations in most of the area appear to have contributed 

 largely to the material of the till. Where the underlying rocks are of a 

 friable nature the material has been reduced to sand or clay and few if 

 any pebbles remain in the till, the coarse and pebbly constituents of the 



