MORAINIC SYSTEMS AT HEADS OF LAKE MICHIGAN AND SAGINAW BASINS. 217 



neighboring lower portions of the morainic system, for the latter bear usually sharp knolls and 

 ridges. 



Among the places where knobs rise 60 to 80 feet above border portions of the moraine may 

 be mentioned Watson Township, Allegan County; the vicinity of Great Bear Lake in Van 

 Buren County; a strip on the south side of Paw Paw River from near Lawrence nearly to Paw 

 Paw, and several places along the eastern border of the morainic system in Berrien and Van 

 Buren counties. 



Swamps are very common among the morainic knolls in the Michigan portion, there being 

 usually several in each township. Most of the lakes are small, few exceeding a square mile in 

 area, though if the bordering swamps are included some of them cover 2 or 3 square miles. 

 Lakes are especially conspicuous along the eastern border of the morainic system and in neigh- 

 boring parts of its outwash gravel plain. 



From northern Allegan County northward to Grand River the morainic tracts are traversed 

 by lines of glacial drainage that break their continuity. The morainic system is also completely 

 cut through by Rabbit River, a tributary of the Kalamazoo heading in northeastern Allegan 

 County. The larger streams, Kalamazoo, Paw Paw, and St. Joseph rivers, all cut through the 

 morainic system and each is bordered by broader terraces and has a valley wider than seems 

 likely to have been produced by the postglacial drainage. The Kalamazoo, however, makes its 

 passage in a rather narrow valley. The several valleys seem to have been utilized as lines of 

 glacial drainage. 1 



STRUCTURE OF THE DRIFT. 



THICKNESS. 



Along the entire course of the Valparaiso morainic system in Indiana and Michigan the 

 drift is very thick, probably averaging more than 200 feet, and few wells have reached the rock. 

 The greatest thickness reported is at Laporte, where 295 feet of drift was found. Rock surface 

 is in places only about 400 feet above sea level, and nowhere seems to reach 700 feet; it is known 

 to rise above 600 feet only in northern Allegan County and in neighboring parts of Kent and 

 Ottawa counties. 



A considerable portion of the drift is probably of pre- Wisconsin age, but the records ob- 

 tained do not afford as a rule criteria for separating the earlier from the later deposits. The 

 thickness of the Wisconsin drift probably does not greatly exceed the measure of the outer 

 border relief of the moraine except in places where the gravel filling on that border has been 

 great. The gravel filling is of little consequence in northeastern Illinois and in Lake and Porter 

 counties, Ind., but farther east and north it is of considerable depth. The relief hi Illinois is 

 estimated to average about 65 feet. The average thickness of the Wisconsin drift may be 

 somewhat less than the relief since the moraine is lower and the drift probably thinner on the 

 borders than along the main crest. In all probability the thickness of the Wisconsin drift is as 

 great along the portion of this morainic system in southwestern Michigan as in northeastern 

 Illinois. 2 



COMPOSITION. 



The drift shows interesting changes in structure along the course of the Valparaiso morainic 

 system from Illinois into Indiana and Michigan. In Illinois the Wisconsin drift is mainly a 

 blue clayey till similar to that forming a considerable part of the Wisconsin drift in Wisconsin. 

 Eastward into Indiana till continues to predominate over sand and gravel only about to the 

 meridian of Valparaiso, beyond which to the northeast sand and gravel greatly predominate 

 over the till. The prominent portions of the morainic system appear to contain a larger propor- 

 tion of sand and gravel than the lower areas, not only in Porter and Laporte counties, Ind., but 

 also hi Michigan; wells that penetrate nothing but sand and gravel for 100 feet or more are not 



1 For a detailed description of the portion of this morainic system in Allegan, Van Buren, and Berrien counties, Mich., see Mon. IT. S. Geol- 

 Survey, vol. 38, 1899, pp. 348-353. 



2 A list of 68 borings along the Valparaiso morainic system in northeastern Illinois, northwestern Indiana, and southwestern Michigan is pre- 

 sented in Mon. U. S. Geol. Survey, vol. 38, 1S99, pp. 354-355. 



