MOKAINIC SYSTEMS AT HEADS OF LAKE MICHIGAN AND SAGINAW BASINS. 211 



in depth from a few inches on the crest to several feet on the less abrupt portions of the slope. 

 The longitudinal vertical section shows that the beds both of the sand and the gravel have a 

 nearly horizontal stratification, though they arch and sag slightly at intervals. Cross-bedding 

 occurs only in thin beds and is not extensive. A transverse section near the southern end of 

 the gravel pit shows evidence of gouging and subsequent refilling; the gravel beds break off 

 suddenly on the east to a depth of 15 feet or more and are replaced by sand. In places the 

 gravel has been taken away completely by the railway company and only a nearly perpendicular 

 wall of sand remains. The sand beds dip rapidly toward the eastern edge of the ridge, but 

 the gravel beds are nearly horizontal. 



The coarse pebbles, cobbles, and bowlderets in this esker, as well as in others studied in 

 Michigan, are mainly of local rock material, which here is a sandstone of Carboniferous age. 

 The liner pebbles are less conspicuously local and embrace rocks of various classes. Increase in 

 angularity is accompanied by decrease in size, large pebbles being well rounded and pebbles one- 

 half inch or less in diameter more or less angular. Of 91 pebbles whose diameter averages less than 

 one-half inch, 32 were of crystalline rocks, largely granites, and the remaining 59 were sandstone, 

 limestone, and chert, principally of local derivation. Of 374 pebbles classified whose diameter 

 averages less than one-fourth inch, 134 were of crystalline rocks and the remaining 240 of the 

 same classes as those of the other group. Much significance is attached to the fact that the 

 coarse pebbles are so largely of local derivation; for if, as some suppose, eskers were formed 

 by superglacial streams, they would have contained less local material (this being for the most 

 part beyond their reach) , and the coarse rocks would be largely of granites and other distantly 

 derived material which had been brought to the surface by ablation. 



Several small gravel pits revealed features similar to those in the large pit. In some of 

 them — for example, in the pit on the line of sees. 9 and 16, Vevay Township — the gravel 

 beds showed a marked southward dip. In the pit at Holt station the beds dip perceptibly 

 toward the eastern edge of the ridge. 



In the plexus of ridges at the southern end of the esker more or less clay is mixed with the 

 sand and gravel, and in places the material exposed appears to be partly assorted till. The 

 flow of water seems to have been less vigorous than in the linear portion of the esker. 



WILLIAMSTON-DANSVILLE ESKER SYSTEM. 



The Williamston-Dansvillc esker system (see PI. IX) consists of a main chain of ridges leading 

 from near Williamston, Ingham County, southward past Dansville, a distance of about 10 

 miles, and of two tributary chains of ridges, one leading southeastward from sec. 16, Wheat- 

 field Township, to join the main chain at the Deer Creek valley in sec. 27, a distance of about 

 3 miles, and the other following the valley of Doan Creek in a course west of south from sec. 

 19, Leroy Township, to sec. 23, Ingham Township, a distance of 8 miles. This last chain is 

 interrupted by a gap of fully 2 miles in the northeast part of Ingham Township. A plexus 

 of sharp gravel knolls is developed at the southern end of the esker sj^stem, which is at the 

 northern edge of the Charlotte morainic system. 



A portion of this esker system, as already noted, was studied by C. C. Douglas x about 1839. 

 The present writer studied the southern part in 1887 but did not trace out the esker system 

 completely until the summer of ]900. 



The main esker heads a mile west of Williamston near the south bluff of Cedar River in a 

 prominent ridge 30 to 35 feet high. This follows the west side of the Deer Creek valley southward 

 through sec. 2, Wheatfield Township, but takes a more direct course west of it in sees. 10 and 

 15. In the last two sections its general height is 15 to 25 feet, but in sec. 15 it consists only 

 of a string of knolls broader than the ridge. For the next 2 miles it follows the Deer Creek 

 valley along the line of sees. 22 and 23, 26 and 27, reaching a height of 50 feet in places in the 

 second half of the distance. In sec. 34 it continues prominent, ascending about 30 feet from 

 the creek valley to a till plain on the east, above which it rises 25 to 30 feet. In the south 

 part of sec. 34 it descends into a swampy sag or esker trough and follows it past Dansville to 



i Op. cit., p. 67. 



