SAGINAW LOBE. 



133 



BOWLDERS. 



Surface bowlders are numerous north of the Tippecanoe, averaging perhaps 1,000 to the 

 square mile on all the dry land of the district. They seem fully as abundant on the gently 

 undulating tract between Tippecanoe and Yellow rivers as on the Maxinkuckee moraine but 

 are rare in the swamps, perhaps because buried underneath the muck and organic growths. 

 Most of them are of granite, but a very few, not more than a fraction of 1 per cent of those 

 exposed, are of a red, jaspery conglomerate. They are generally small enough to be easily 

 gathered up or buried by the residents, their common diameter being 2 to 3 feet. 



In the district south of the Tippecanoe the drift in the undulating belts as well as in the 

 plains is largely a clayey till. It is not rare, however, to find small knolls and ridges of sand 

 or sandy gravel on prominent points or capping till swells. Few, however, contain gravel 

 suitable for road ballast, and some seem to contain no pebbles. 



South of the Tippecanoe bowlders are abundant only in certain belts, one running south- 

 ward to Kewanna from the Tippecanoe Valley, and another running northeast and southwest 

 through southern Fulton and northern Cass counties. (See PL VI.) In the former bowlders 

 are no more conspicuous than in the district north of Tippecanoe River; in the latter they are 

 much more numerous, numbering several thousand to the square mile. Granite far outnumbers 

 all other kinds. The common diameter, as in the district north of the Tippecanoe, is 2 to 3 

 feet ; those exceeding 5 or 6 feet are rare. 



THICKNESS. 



Depth to rock. — In the district occupied by the Maxinkuckee moraine and associated 

 bowlder belts and undulating tracts the drift is very thick. The least thickness reported is 90 

 feet (at Royal Center) and the greatest thickness may exceed 300 feet. Reported thicknesses 

 are set forth in the following table : 



Deep borings on or near Maxinkuckee moraine. 



Altitude 

 of rock 

 surface. 



South Bend 



Plymouth , 



Lake Maxinkuckee (Moorman boring) 



Rochester 



Warsaw 



Warsaw, 3 miles west of. 



Kewanna 



Royal Center 



If the rock surface has the same altitude beneath the Penn geodetic station, 3 miles south- 

 east of South Bend, as at South Bend the thickness at the former place is over 300 feet. If it 

 is the same on the crest of the moraine west of Plymouth as at Plymouth the thickness is about 

 300 feet. 



If the rock is as low under the hills east of Maxinkuckee Lake as in the Moorman boring at 

 the lake, the drift on the hills exceeds 324 feet, for the Moorman boring on ground only 20 feet 

 above lake level failed to reach rock at a depth of 203 feet. 



Probably a considerable part of the drift was deposited before the Wisconsin stage of 

 glaciation, but the data concerning the character of this deeper part are insufficient to fix its 

 contact with the Wisconsin drift. 



The relief of the moraine above the districts to the west seems to be entirely due to Wiscon- 

 sin drift, and this would justify the reference of between 50 and 100 feet of drift to this latest 

 stage of glaciation. The depth of Lake Maxinkuckee (80 to 90 feet) carries its bed below the 

 level of the plain outside the moraine and suggests that considerable filling may have occurred 



