232 PLEISTOCENE OF INDIANA AND MICHIGAN. 



eastern ridge are thickly set with basins 50 feet or more in depth. A few points on each ridge 

 rise considerably above the general level, but much of their surfaces is gently undulating. 



The drift of the valley-like depressions between the ridges is sandy and rather low in fer- 

 tility, and consequently scarcely any of the lowland has been brought under cultivation. These 

 plains have a southward slope and were apparently utilized by lines of glacial drainage flowing 

 southward as far as Grayling. Thence the drainage appears to have been westward down the 

 Manistee, for a well-defined channel leads from the Au Sable westward past Portage Lake to 

 the Manistee and is continued along the Manistee Valley. These features indicate that the 

 border of the Michigan ice lobe had withdrawn to the north side of the west-flowing part of 

 Manistee Eiver in Kalkaska, Grand Traverse, and Wexford counties at the time these ridges 

 were being formed. The Au Sable at that time appears to have been covered by the ice from 

 the Huron basin at least as far up as western Oscoda County. These ridges seem to be some- 

 what younger than the system south of Au Sable River in southern Crawford County, for that 

 system is apparently continued south of Manistee River. Their correlative is probably found 

 in a fragmentary chain of knolls and ridges along the north side of the Manistee Valley. 



To the east, north of the Au Sable River, lie extensive sandy plains which bear many 

 basins and some knolls and short ridges. The best-defined ridge lies northwest of Mio; it is 

 of crescent form, curves to the west, and is bordered by a till plain on the east and south. A 

 small lobe of ice seems to have protruded eastward into the Au Sable Valley when this ridge 

 was formed. Near the middle of the ridge, at a point about 6 miles north of Mio, a prominent 

 point rises about 150 feet above the surrounding country, but elsewhere the relief is only 50 to 

 75 feet. 



WEST BRANCH-GLADWIN GROUP OF MORAINES OF THE WESTERN LIMB OF 



THE SAGINAW LOBE. 



By Frank Lbverett. 



GENERAL FEATURES AND DISTRIBUTION. 



The moraines formed by the Saginaw lobe in its recession from the Charlotte morainic 

 system and prior to the readvance marked by the Port Huron morainic system are crowded 

 closely together in the reentrant angles between the Saginaw and Lake Michigan lobes on the 

 one hand and between the Saginaw and Huron-Erie lobes on the other, but are more widely 

 spaced around the end of the Saginaw lobe. They are much more numerous south of the 

 Grand River outlet than they are north of that outlet. The small moraines that branch from 

 the northern portion of the western limb and bridge the reentrant between it and the Lake 

 Michigan lobe are exceptionally complex and have already been treated (pp. 229-231). Here 

 only the moraines along the Saginaw lobe north of the Grand River outlet are discussed; those 

 at the end of the lobe and those on its eastern side are discussed later by Mr. Taylor (pp. 238-244). 

 The western limb of the Saginaw lobe has strong development as far northeast as the bend of 

 Au Sable River in Alcona County. 



The portion of the bulky series of moraines between Au Sable River and Harrison, termed 

 the West Branch morainic system, is 4 to 8 miles in width. (See PI. VII, in pocket.) It 

 follows the line of Oscoda and Ogemaw counties westward from Au Sable River for about 15 

 miles, runs southward for an equal distance through central Ogemaw County, turns southwest- 

 ward near West Branch, and continues for about 30 mdes across southeastern Roscommon and 

 northwestern Gladwin counties to Harrison in Clare County. There is some development of 

 parallel ridges separated by narrow gravel plains or lines of glacial drainage in the portion 

 between West Branch and Harrison, but northeast from West Branch there is only a single 

 massive moraine. 



In southern Clare County the West Branch morainic system separates into an outer strong 

 moraine and an inner relatively weak one. The outer moraine, however, becomes separated 

 a few miles farther southwest, in eastern Mecosta County, into two moraines, each of consid- 

 erable strength. These two moraines bear southeastward across southwestern Isabella County 



