232 THE ILLINOIS GLACIAL LOBE. 



drift ridges before water can be obtained, while in Indiana, water-bearing 

 beds are usually found before reaching the base of the ridges. 



This morainic system is characterized by a limited number of surface 

 bowlders, and a moderate number are incorporated with the till. The 

 majority of the surface bowlders are crystalline rocks of Canadian deriva- 

 tion. They are usually subangular and seldom show striated faces. As in 

 the drift sheets of this region generally, the bowlders incorporated in the 

 till appear to be much more frequently glaciated than those on the surface. 

 There is also apparently a larger proportion of limestone rocks of local or 

 semilocal derivation embedded in the till than are found on the surface. 1 



Several large blocks of limestone, however, were found on the surface 

 in Champaign County, Illinois. At George Stewart's, a few miles southeast 

 of Philo, on a prominent portion of the ridge in sec. 4, T. 17, R. 10 W., two 

 large limestone blocks were examined by the writer. They are of gray 

 color and contain Pentamerus shells, apparently of Niagara age. Mr. 

 Stewart has dug to a depth of about 4 feet at the side of one of the rocks 

 without reaching its base, and it has a surface exposure nearly 10 feet 

 square. The other block has been uncovered for a space of about a square 

 rod and extends some distance beneath the ground. The nearest known 

 outcrop of this rock formation toward the north (the direction from which 

 the ice came) is in northern Iroquois County, some 60 miles distant. 



In Indiana the district traversed by these moraines and the morainic 

 ridges themselves are characterized by few surface bowlders, except in north- 

 western Montgomery and northeastern Fountain counties. They there 

 abound on the plains as well as on the ridges. It seems probable, however, 

 that these bowlders are to be connected with the late Wisconsin ice invasion, 

 though their position is such as to throw them outside a regular border of 

 the ice sheet, The bowlders apparently connect on the north with well- 

 defined bowlder belts of late Wisconsin age which lead northward from the 

 Wabash River near Williamsport. Whether the bowlders on the group of 

 knolls near Rob Roy referred to above were deposited by this' later invasion 

 is uncertain. It is also not entirely certain that these knolls are independ- 

 ent of the later invasion. 



The surface of the ridges of the Champaign morainic system, as well 

 as the plains between them, is commonly covered with a pebbleless clay 



'For discussion of these features see Chamliorlin : Jour. Geol., Vol. 1, 1893, pp. 47-60. 



