248 PLEISTOCENE OF INDIANA AND MICHIGAN. 



The percentage of crystalline material from Canadian sources is relatively small in the 

 surface parts of the drift, probably more than 90 per cent of the general drift mass being derived 

 from the Paleozoic rocks, mostly from near-by sources. 



In several places, as below the asylum southwest of Ionia and at the brickyards 2 miles 

 east of Lansing, pebbleless clays, evidently deposited in lake waters, appear to have been over- 

 ridden by later ice advances. Those near Ionia are deeply buried under till. Those east of 

 Lansing are overlain by thin, patchy till with bowlders. It seems probable that the lake waters 

 in which these clays were deposited were temporary local bodies of relatively small extent. 



ASSOCIATED TILL, PLAINS. 



The deployed slender moraines he in roughly parallel lines, except in the region of over- 

 lapping east of Lansing, and the intervals between them vary from 1 to 6 miles in width. The 

 till plains which lie between the moraines are long narrow strips of irregular width and are 

 generally typical of their kind. They are plains of clay, more or less pebbly and stony, and 

 have generally a smooth surface which, although flat and apparently level, is nearly everywhere 

 slightly inclined in one direction or another. 



The inclination of the till plains depends chiefly on the general slope of the region. Under 

 normal conditions of deposition in a fiat region the terminal moraines are heaped up in ridges 

 and the till plains slope gently backward from them in the direction in which the ice retreated. 

 The surface of each till plain is therefore normally highest at the inner edge of the moraine 

 with which it is associated and lowest immediately in front of the next succeeding moraine. 

 The terminal moraine is a heaped-up marginal deposit of till, and the till plain or ground 

 moraine is a subglacial formation spread in a smooth and relatively thin sheet under the 

 weight of the moving ice. The till plains are composed mainly of bowlder clay, but they have 

 few bowlders on their surface or in the sections that show their structure. 



The till plain in front of the Lansing moraine slopes gently southward. This plain belongs 

 to the heavier morainic belt (Charlotte morainic system) south of the deployed group. 



The till plain on the inside of the Lansing moraine has no well-defined general direction 

 of slope but is inclined slightly in different directions in different parts. The remainder of the 

 till plains back to the shores of glacial Lake Saginaw all slope gently back from the moraines 

 with which they are associated, except in a few localities, such as south of St. Johns, where the 

 plain slopes south and thus guided a glacial river through a gap in the Fowler moraine. After 

 passing through this moraine, the river crossed the next till plain inside the Lyons moraine 

 instead of going northwestward to the Grand River channel south of Matherton. For 10 miles 

 west of Bancroft the Looking-glass glacial river flowed in the till plain of the Lyons moraine, 

 most of the way close back of the moraine rather than farther north. 



The till plains are all essentially the same in the remainder of the district back to the beaches 

 of glacial Lake Saginaw. In the eastern part of Genesee County the shallow basins across which 

 the moraines were built led to the formation of shallow glacial lakes like Davison and Kersley 

 (pp. 252, 254), where the till plain dipped to a lower level along a part of its length. 



Below the Arkona beaches the slender moraines are water-laid and on that account present 

 little or no contrast with the till plains; and further, they were nearly leveled by the severe 

 wave erosion. 



The whole region below the Arkona beaches is a plain without prominent features, the 

 higher parts carrying scattered bowldery patches marking the remains of moraines. The lower 

 part outside of the Port Huron morainic system and comprising the central part of Saginaw 

 County is a plain of faintly laminated lake clays, containing few pebbles or coarse material. 

 In texture they are waxy and apparently as fine grained as cocoa butter. Shafts sunk for coal 

 ruining have passed through these clays at a number of places, one at St. Charles penetrating 

 them to a depth of 90 feet. 



