154 PLEISTOCENE OF INDIANA AND MICHIGAN. 



STRUCTURE OF THE DRIFT. 

 COMPOSITION. 



The drift of the Tekonsha moraine is generally loose textured even where not assorted. 

 The looseness naturally results from the presence of much sand derived from the underlying or 

 neighboring sandstone formations, as well as from the action of water and the removal of finer 

 material during deposition. The nearest approach to clayey till noted is in western Calhoun 

 County, a few miles south and southwest of Battle Creek, where the moraine laps upon a clayey 

 plain that extends into eastern Kalamazoo County. The principal tracts of beech and maple 

 timber are found here. There is ordinarily much diversity of structure within even small areas. 

 On a single farm one well may be largely in sand or gravel, another in a loose-textured till, and 

 a third in a combination of the till with sand and gravel. The interlobate spur north of Kala- 

 mazoo River is largely sand and gravel. 



BOWLDERS. 



Bowlders are very numerous over nearly the whole surface of the moraine and are also 

 embedded in the drift, for nearly every cutting observed is full of them. They are least con- 

 spicuous on the interlobate spur north of Kalamazoo River. The bowlders are such an encum- 

 brance that piles of them appear in nearly every field and several miles of fences are built of 

 them. Places near Hog Creek in northeastern Branch County were estimated to carry 1,000 

 bowlders to the acre and some knolls in that vicinity are literally covered with them. Many of 

 the bowlders are large enough to be shaped into building stone. The smaller ones are useful for 

 checking the gullying of hillside slopes when thrown into ditches and are thus easily buried. 

 The majority of the bowlders are well rounded, probably by exfoliation, and few show striated 

 surfaces. As hi the moraines to the southwest, granite rocks greatly predominate, but quartzites 

 and quartzitic conglomerates abound and numerous other rocks are represented. Local sand- 

 stone in mass is rare on the surface, though blocks as well as small pieces abound within the drift 

 sheet. 



THICKNESS. 



Relation to table-land of sandstone of the Marshall formation. — Compared with the drift in the 

 district outside or southwest of the moraine, the drift of the Tekonsha moraine is very thin. 

 This is due to the position of the moraine, which stands on the edge of the table-land of sandstone 

 of the Marshall formation, whose rock surface is much higher than that of the adjacent lowland 

 underlain by the Coldwater shale. The sandstone table-land has an altitude of 900 feet or more 

 in Calhoun and eastern Branch counties, and some of its highest points exceed 1,000 feet. Ac- 

 cordingly, in numerous places along the moraine rock is struck at 50 feet or less, and in the dis- 

 trict north of Quincy it stands above the level of some of the sags or channels in the moraine. 

 The table-land is interrupted more or less by deeply eroded preglacial valleys that lead into the 

 lowland to the southwest and at such places the drift must be very thick, presumably 200 feet 

 or more, for much of the outlying lowland is at least 200 feet lower than the table-land. The 

 table-land extends slightly into the eastern edge of Kalamazoo County south of the river near 

 Climax but seems to be interrupted by a deep valley in the vicinity of the river. Borings in and 

 near Augusta reach a level 100 feet below the present stream without encountering rock, one 

 boring being 150 feet and another on higher ground 220 feet. 



Well data. — The following record of one of the deep wells near Augusta was obtained from 

 the driller. The well is on the Colchester farm on the northwestern outskirts of the village, at an 

 altitude perhaps 120 feet above Kalamazoo River. Water rose within 70 feet of the surface. 



Record of Colchester uell near Augusta, Mich. 



Feet. 



Gravelly or sandy material with thin beds or partings of clay 140 



Clay, blue, rather compact (probably pre- Wisconsin) 80 



Cement crust above water bed. 



220 



