POST HURON MOEAINIC SYSTEM AND PROBABLE CORRELATIVES. 303 



ward to the base of the Green Bay peninsula, where it curves back to the southwest and north 

 into the Lake Winnebago basin, passing to the south end of that lake. Its course has not been 

 fully determined from Lake Winnebago northward, but it probably correlates with a moraine 

 which crosses the State line of Wisconsin and Michigan east of Florence, Wis., and runs north- 

 ward along the east side of Michigamme River about to the latitude of Channing, where it turns 

 westward at a reentrant between the Green Bay lobe and the more western portion of the ice 

 field. Studies in 1910 in the Northern Peninsula of Michigan, northern Wisconsin, and north- 

 eastern Minnesota seem to give warrant for correlating this morainic system with one which 

 sweeps around the head of Lake Superior, but the facts can be fully established only by further 

 field work. 



Present knowledge at least suggests that the glacial readvance marked by the Port Huron 

 morainic system continued all the way from New York to Minnesota or entirely across the 

 Great Lakes basins. A similar readvance is indicated in the ice field which covered the 

 Red River basin west of the Great Lakes, a basin which subsequently held Lake Agassiz. 



TOPOGRAPHY. 



CHARACTER. 



Considerable variation is displayed by this morainic system in its circuit of the northern 

 Huron and northern Michigan basins. On the slope toward the Huron basin lie great morainic 

 spurs extending toward the lake from the outer ridge of the system and isolated island-like 

 tracts of moraine surrounded either by sand or till plains. (See PI. VII.) In Oscoda County, 

 and to some extent in Otsego County, plains separate the spurs or transverse ridges from 

 the outer ridge of the system, but in the intervening district in Montmorency County the spurs 

 are very closely connected with the outer moraine. Toward Lake Huron from this outer 

 moraine the ridges become less closely aggregated and much of the surface is occupied by till 

 and sand plains. 



In the reentrant angle between the Huron and Michigan lobes in northern Otsego and 

 eastern Charlevoix counties morainic topography is prominently developed as far north as 

 the lowland which leads from Little Traverse Bay eastward to Burt Lake, and very prominent 

 morainic tracts extend north of this lowland, one of them reaching the shore of Lake Michigan 

 north of Little Traverse Bay. 



This morainic system on the slope toward Lake Michigan and Grand Traverse Bay differs 

 in one striking particular from its expression on the slope toward Lake Huron. The outer 

 moraine of the Lake Michigan portion is a distinct narrow ridge paralleled throughout much 

 of its length by a second definite ridge, from which it is separated by the outwash and border 

 drainage connected with the second ridge. Morainic spurs such as occur on the Huron slope 

 are also conspicuous on the Lake Michigan slope, but they are related to the second instead 

 of to the outer ridge of the system. The striking parallelism of these ridges is thought to indi- 

 cate that the second ridge is a close successor of the outer one and a part of the same system. 



The second ridge is practically continuous from eastern Charlevoix County southwest- 

 ward to the head of Grand Traverse Bay. Southwest from Grand Traverse Bay, however, it 

 consists of a broken chain of ridges leading across eastern Benzie County through an extensive 

 gravel plain, from the western side of which prominent transverse ridges extend across south- 

 western Leelanau, Benzie, and Manistee counties to the shore of Lake Michigan, southwest- 

 ward from Little Traverse Bay to Grand Traverse Bay, and on the borders of the latter con- 

 spicuously developed drumlins and drumlinoidal ridges lead either into the second moraine or 

 somewhat later morainic ridges on the inner border of that moraine. 



On the Huron as well as the Lake Michigan slope great depressions extend back between 

 the morainic spurs and transverse ridges to the inner border of this morainic system. Several 

 on the Lake Michigan slope are occupied by narrow, deep lakes, and such lakes also occur on the 

 Huron slope in Cheboygan County and northern Alcona County, but others are occupied by 



