MORAINIC SYSTEMS AT HEADS OF LAKE MICHIGAN AND SAGINAW BASINS. 205 



TOPOGRAPHY. 



Along much of the morainic system, and especially in the portion distinct from the Lake 

 Michigan and Huron-Erie lobes, the topography is of a swell and sag type, with many separate 

 knolls 10 to 20 feet in height and some in groups or chains 50 to 75 feet in height. The relief 

 above the outer border plain is slight, for a basement ridge is generally lacking and the 

 moraine is merely an assemblage of knolls and sags. In the reentrant angles between the 

 Saginaw and Lake Michigan lobes and between the Saginaw and Huron-Erie lobes there are a 

 few very prominent knolls ranging from 100 to 200 feet in height. Dias Hill rises to 1,032 feet, 

 or nearly 200 feet above the surrounding country, hi an irregular mass covering scarcely 2 square 

 miles. A range of hills east of Rockford, hi north-central Kent County, known as the Prospect 

 Hill Range, is about 100 feet in height, 3 miles in length, and less than one-half mile in width. 

 Another range about 8 miles farther north, lying east of Cedar Springs, is of similar dimensions 

 to the Prospect Hill Range. These are the principal prominent elevations in the vicinity of 

 the Michigan and Saginaw reentrant. 



Eastward from the reentrant the first prominent group of knolls is on the east side of 

 Thornapplc River. It begins opposite Middleville and extends northward about 7 miles. Its 

 height is about 100 feet above the highest terrace of the Thornapple and in several points 

 exceeds 900 feet above sea level. It trends at a right angle to the moraine and stands in the 

 direct line of continuation of the prominent mterlobate spur between the Lake Michigan and 

 the Saginaw parts of the Kalamazoo morainic systems. This relation has suggested the possi- 

 bility of its behig an overridden part of the interlobate spur, though full evidence to that effect 

 has not been found. From 3 to 6 miles east of this range other prominent hills are arranged 

 in small groups whose highest points considerably exceed 900 feet. The surrounding morainic 

 tracts rise to about 850 feet. 



Immediately north of Hastings the moraine is traversed by a chain of lakes which leads 

 across it nearly at right angles. Most depressions of this sort have been utilized by rivers as 

 passages, but this one is not so occupied. 



The Thornapple Valley, which lies between the two members of the morainic system in 

 eastern Barry and western Eaton counties, is fully 100 feet below the bordering moraines and 

 nearly a mile hi average width, yet it seems to have suffered only a small amount of erosion 

 either by the present river or by its fhivioglacial predecessor. It is merely a large depression 

 left by the ice. 



The portion of the morainic system south of Thornapple River is deeply indented by long 

 depressions which extend from north to south nearly through it and whose bottoms are but 

 little above Thornapple River. Some short gravelly ridges of esker type lie in these depres- 

 sions. A similar deep depression traverses the moraine on the north side of the river immedi- 

 ately west of Vermontville, and this also carries esker-like gravel ridges. 



From Vermontville eastward across Eaton County to the Grand River valley near Eaton 

 Rapids (see Lansing topographic sheet) the inequalities of surface are due more largely to deep 

 depressions in the morainic system than to prominent knolls, though there is a knoll just north 

 of Charlotte about 75 feet in height and several along the Grand River valley below Eaton 

 Rapids 40 to 50 feet in height. Some of these depressions parallel the trend of the moraine, 

 thus separating it into a system of parallel belts, but some lead directly across one or more 

 of the morainic members. These depressions are largely occupied by swamps. Some have 

 evidently been utilized by lines of glacial drainage, but others still preserve the irregularities 

 of contour left by the ice sheet. In one there is an esker whose southern terminus is at the 

 city of Charlotte. (See p. 209.) 



East of Grand River in southern Ingham County (see Mason topographic sheet) the 

 moraines are combined into a single belt, whose borders are very irregular both on the north 

 and the south. The north border is deeply indented by swampy tracts, some of which extend 

 nearly through the morahiic belt. Some of these are occupied by eskers which head on the 

 till plain north of the moraine. The. south border shows some recesses, one of which contains 



