176 PLEISTOCENE OF INDIANA AND MICHIGAN. 



above the gravel plain which lies between them, except in the district from Dowagiac south- 

 west to St. Joseph River, where the inner ridge and the. gravel plain drop nearly 100 feet below 

 the crest of the outer ridge. The relief on the inner or western border of the inner ridge is 

 about 200 feet throughout its entire course from Barry County to Dowagiac, the plain west 

 of the ridge being about 750 feet and the ridge nearly 950 feet, but from Dowagiac to Niles 

 the relief on this border is reduced to about 50 feet and it exceeds 75 feet in but few points 

 in the tract west of St. Joseph River. 



CHARACTER. 



Outer ridge. — Along the entire length of the outer ridge, basins as well as sharp knolls 

 are conspicuous. Many of the knolls stand 50 to 75 feet above the neighboring basins, 

 but only 25 to 50 feet above the bordering outwash apron, below which many basins are sunk 

 25 feet or more. Many of the basins are occupied by ponds or small lakes, though most of them 

 are either dry or have been sufficiently filled to be largely occupied by vegetation. The gravel 

 plain between the two ridges contains a number of lakes, some of which are one-half mile or more 

 in width and nearly fill the space between the ridges. The great majority, however, are only a 

 few acres in extent and some are but a fraction of an acre. On the west border of the outer 

 ridge for a few miles in the southwest portion in Cass County, Mich., and St. Joseph County, 

 Ind., there is a steep bluff 50 to 100 feet in height which apparently was produced by border 

 drainage along the front of the ice when it had receded a short distance west of the moraine. 

 Elsewhere the inner or west face of the outer ridge carries knolls and basins down to the level of 

 the gravel plam which separates it from the western ridge. In places in the vicinity of the State 

 line the outwash apron extends back into the ridge for a mile or more, and in a number of 

 places basins occupied by small lakes cause slight irregularities, but as a rule the front of the 

 moraine is remarkably regular. 



Inner ridge. — The inner or western ridge is much more broken by deep depressions than the 

 outer. These depressions open westward into the inner border district, which, as already stated, 

 is nearly 200 feet lower than the crest of the ridge. The eastern border of the ridge, however, 

 shows only slight irregularity, and the basins are usually only 25 to 35 feet below the level of 

 the gravel plam between the two morainic ridges. The inner ridge has its greatest width imme- 

 diately northeast of Dowagiac, where narrow gravel plains associated with the moraine lead 

 to the larger gravel plam outside. Immediately south of Decatur the gravel plam for 2 or 3 

 miles virtually takes the place of the inner ridge, being built to a level nearly as high as the 

 neighboring parts of the moraine. 



A conspicuous depression or fosse, one-fourth to one-half mile wide and 20 to 25 feet deep, 

 lies between the inner ridge and the gravel plain immediately east and south of Dowagiac. 

 The gravel plain stands like a bluff on the southeast border of this fosse or depression, but the 

 ridge on the west is very inconspicuous, few of its knolls being more than 10 or 15 feet hi height 

 and its crest being scarcely as high as the gravel plain. 



The inner ridge in the bend of St. Joseph River west of Niles reaches an altitude only a few 

 feet higher than that of the gravel plam on its south border, but knolls in it are 30 to 40 feet above 

 neighboring sags and basins. It is much broken by basins near the State line and southward 

 to Warren, Ind. Several of the basins contahi lakes. The knolls are rather sharp or steep 

 sided throughout this section west of St. Joseph River. On its western or inner face near 

 Buchanan, Mich., a steep bluff 30 feet or more in height has been formed, apparently by border 

 drainage. The ice approached this place very closely while forming the Valparaiso morainic 

 system. Whether the cutting of this bluff occurred immediately on the withdrawal of the 

 ice from the Kalamazoo system or at a later time during the development of the Valparaiso 

 system, has not been clearly worked out. 



The topography of Sumption and Rolling prairies, as already indicated, is more like that of 

 the neighboring gravel plains than of the Kalamazoo morainic system. Basins are conspicuous, 

 but knolls and ridges of strong expression are wanting. In places a slight undulation of surface 

 is visible, but it amounts to scarcely 15 feet in vertical range. 



