MORAINIC SYSTEMS AT HEADS OF LAKE MICHIGAN AND SAGINAW BASINS. 209 



to render it probable that they owe their origin to the same agency — subglacial drainage. In 

 a few places two eskers unite to form a single ridge. (See pp. 21 1-212.) All eskers of sufficient 

 length are represented on the glacial map and will be considered in turn from Charlotte east- 

 ward. Eskers only a fraction of a mile in length will be passed over with a mere mention. 



CHARLOTTE ESKER. 



This esker, which has its terminus at the eastern edge of the city of Charlotte, is about 9 

 miles hi length. Its northern end is in sec. 3, Benton Township, on the north side of the Thorn- 

 apple River valley. The river passes across its line in the edge of sees. 10 and 15. The esker 

 follows up the south fork of Thornapple River to the Grand Trunk Railway, about 1J miles 

 southwest of Potterville. Thus far the esker is represented by short ridges separated by gaps 

 nearly as long as the separate ridges, but from the railway southward, across sec. 34, Benton 

 Township, it is more nearly continuous as a low winding ridge 15 to 20 feet in height and 90 

 to 100 yards in width at its base. A few short spurs lead from it to the border of the trough in 

 which it lies. In Eaton Township it is well developed in the north part of sec. 4 ; for the next 

 mile southward it is much interrupted; and after this it is again continuous for a mile or more. 

 Its southern terminus is a well-defined fan-shaped sandy delta which covers about 3 square 

 miles immediately east of Charlotte. Wells in this delta penetrate a fine gravel with much 

 sand intermixed throughout its entire depth to the underlying sandstone. The sandstone has 

 an uneven surface, the depth to it ranging from 16 to 60 feet. 



Slight excavations in the esker near its north and south ends show it to be composed mainly 

 of gravel of medium coarseness. The pebbles are largely sandstone of local derivation. 



The well-defined trough, hi which the esker lies from its head to its southern end, shows a 

 slight descent to the Thornapple Valley and then a slight rise to the delta at Charlotte. At its 

 lowest part its altitude is about 850 feet above sea level, and at the esker fan it is approxi- 

 mately 900 feet. Its depth is from 10' to 20 feet and its width from one-eighth to one-fourth 

 mile. It passes entirely through the Charlotte morainic belt, the esker fan being at the outer 

 edge of the moraine, and it is in the moraine except for 2 or 3 miles at its northern end, where it 

 is in the inner border till plain. 



MASON ESKER. 



Investigation. — The Mason esker (see PI. VIII), which passes through the city of Mason, 

 the county seat of Ingham County, and the Williams ton-Dansville esker (see PI. IX), which 

 lies a few miles farther east, were each described briefly by C. C. Douglas ' hi 1S39, being among 

 the first of this class of ridges to be described in North America. The Mason esker was also 

 briefly described by L. C. Wooster 2 in 1884. The Mason and Charlotte eskers were studied 

 by the 'writer in the fall of 1887, and the description here given of the Mason esker was prepared 

 by him in the following winter but was never submitted for publication. 



Extent. — The Mason esker is the longest yet observed in Michigan, its length being not 

 less than 20 miles. Cemetery Hill, a prominent gravel knoll 2 miles southeast from the state- 

 house at Lansing, near the mouth of Sycamore Creek, may be regarded as its northern ter- 

 minus. This Mil rises about 60 feet above the bed of the creek on the west and 30 feet above 

 the valley on the east; a few gravelly knolls to the east and northeast form an indefinite north- 

 ward extension. Its southern terminus is in the Charlotte morainic system southeast of Mason. 

 For its entire length it lies hi a well-marked trough. 



Esker trough. — For about 3 miles south from Cemetery Hill the esker follows a depression, 

 one-fourth to one-half mile wide, hi which Sycamore Creek flows. About 1£ miles north of 

 Holt, however, the creek bends abruptly, and the esker trough leaves the creek valley and 

 remains distinct from it for 7 or 8 miles. The esker trough in places has a width of half a 

 mile and a depth of 25 to 30 feet, but within the space of a mile it may contract to 100 to 150 

 yards or may become so shallow that it is difficult to trace. For about 5 miles it maintains 



1 Second Ann. Eept. First Michigan Geol. Survey, 1839, p. 67. 2 Karnes near Lansing, Mich.: Science, vol. 3, 1S84, p. 4. 



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