572 PRE-WISCONSIN GLACIAL DRIFT IN MONTANA v 



their general composition and appearance being almost identical except 

 in this particular. In the older till the crystalline Laurentian pebbles 

 present are so much decayed and friable that they fall to pieces with a 

 light blow from the hammer, while in the upper till they are firm and 

 fresh and practically unweathered. The limestone pebbles, which are 

 fairly abundant in the upper till, are practically entirely leached out of 

 the lower, which is partly indurated in places and deeply iron-stained. 

 The difference in the appearance of these two bands of till is so marked 

 that they can easily be distinguished at a distance of one-fourth to one- 

 half mile. Judging from the amount of weathering present, it seems evi- 

 dent that the time interval between the lower and upper of these two tills 

 is much greater than that between the upper (Wisconsin) till and the 

 present. 



On the whole, it seems reasonable to infer that the lower till here found 

 corresponds to the lower till found on the Belly Eiver at Lethbridge, 

 Alberta, and also probably to the old continental drift found south and 

 east of the margin of the Wisconsin drift in eastern Montana and western 

 North Dakota. 



