LATER MORAINES OF LAKE MICHIGAN, SAGINAW, AND HURON-ERIE LOBES. 231 



the Roscommon-Crawford county line for about 9 miles. It makes a slight offset to the north 

 at the valley of South Fork of Au Sable River but continues westward through southern 

 Crawford County 2J to 4£ miles from the south line of the county. Knolls in southeastern 

 Kalkaska County fill in to some extent the gap between the western end of this ridge and the 

 more massive moraine on the south side of Manistee River. Throughout its length this ridge 

 is narrow, its average width being less than a mile; it is, however, prominent, rising on an 

 average fully 50 feet and in places more than 100 feet above the bordering plains; in a con- 

 siderable jiart of its course it stands above 1,300 feet and at a few points in Ogemaw County 

 1,400 feet or more above the sea. It is composed of loose-textured gravelly drift throughout, 

 but it is on the whole more fertile than the plain on the south, having some fine loamy material 

 mixed with its gravel and coarse material. A productive till plain lies south of this ridge hi 

 the northeast part of Roscommon County, but elsewhere the plain on the south is sandy. 



From the bend of the West Branch morainic system at the line of Ogemaw and Oscoda 

 counties a sharp ridge runs northwestward about 4 miles into Oscoda County. It leads toward 

 ridges lying south and west of Luzerne in the western range of townships of Oscoda County, but 

 is separated from them by a gap 6 or 7 miles wide, containing a sandy plain. Westward from 

 western Oscoda County along the south side of Au Sable River to the vicinity of Grayling a 

 somewhat intricate system of ridges and sand plains occupies a belt about 5 miles wide, about 

 half of which is morainic; the ridges as well as the plains are sandy. 



From the west side of Portage Lake near the west line of Crawford County a strong moraine 

 2 to 5 miles wide leads down the south side of Manistee River to the western part of Wexford 

 County. It rises 100 to 400 feet above the river, its relief being much greater from northern 

 Missaukee County westward than toward Portage Lake. Its altitude is generally a little 

 above 1,200 feet, and hi northern Missaukee County reaches 1,400 feet. The moraine is mainly 

 of loose-textured gravelly drift but includes sufficient fine material along much of its course to 

 make it suitable for agriculture, and it is occupied by several prosperous farming settlements. 

 Tracts of clayey till lie on its inner slope, and narrow plains hi places lie between it and Manistee 

 River. A sandy plain, apparently outwash from the moraine, lies along most of its outer or 

 southern border. 



This moraine unites in western Wexford County with the Harrison-Lake City ridge, and 

 the combined morainic system runs southward into Lake County. It lies along the western 

 edge of the great Saginaw-Lake Michigan interlobate tract in eastern Lake and Newaygo coun- 

 ties, and its southern portion is not easily separated from that tract. Offshoots from it will be 

 considered later. 



RIDGES AT HEADWATERS OF AU SABLE AND MANISTEE RIVERS. 



Tw t o of the headwater tributaries of Au Sable River and the headwater portion of Manistee 

 River lead southward from Otsego County into Crawford County through sags between prominent 

 morainic ridges to the vicinity of Grayling, where the Au Sable turns eastward and the Manistee 

 westward through a sandy plain. The ridges stand 100 to 200 feet above the intervening sags; 

 they are highest at their northern ends, attaining an altitude of fully 1,400 feet; their southern 

 ends are somewhat less than 1,300 feet. The ridges from the west branch of Au Sable River 

 eastward appear to have been produced by ice moving westward from the Lake Huron basin, 

 and those west of this stream seem to have been formed by an eastward movement hi the Lake 

 Michigan lobe. The central ridges were probably formed before those on either side, for the 

 gravel plains or lines of glacial drainage lead toward the central ridges from those on the eastern 

 and western borders of the system. (See PI. VII.) The central ridges have at the surface bowl- 

 dery clay a few feet deep, which was largely covered with maple forest, but which is now being 

 rapidly cleared for farming. Wells indicate that sand sets hi at slight depth, commonly 10 feet 

 or less, and extends as far as the wells have been carried, or to 200 feet or more. The ridges 

 on the eastern edge of the system are more sandy and less suitable for agriculture. The central 

 ridges are on the whole less deeply indented by basms than the later ones. Portions of the 



