TRANSEAUBOGS OF THE HURON RIVER VALLEY 353 



note that a large part of the surface drained by the Huron and its 

 tributaries, before it makes the great bend to the southeast below 

 Portage lake, is made up of sand and gravel, composing and accom- 

 panying the Saginaw-Erie interlobate moraine. It is, a region of 

 steep hills, with occasional dry plains, everywhere penetrated by 

 lakes and swamps. 



The country which the river next crosses, beyond the great bend, 

 for a distance of 20 miles (32 km ) is composed of glacial till plains 

 and clay moraines a belt extending NE-SW, approximately parallel 

 to the interlobate moraine. Here, although the hills are well marked, 

 the slopes are more gradual and the basins broader. The river 

 is bordered by banks several feet in height, and seldom attains a 

 width of 150 feet (so m ). 



The last 30 miles (5o km ) of the Huron River traverses a meander- 

 ing course sunken from 50 feet (i5 m ) at Ypsilanti to 25 feet (7.5) 

 at Rockwood below the surface of a glacial lake plain sloping gently 

 southeastward from the morainic belt just described, to the western 

 shore of Lake Erie. The soil is here composed of sand, sandy loam, 

 and in the vicinity of the lake clay; the only topographic features 

 aside from the sunken water courses being the several beach ridges 

 and dunes marking the successive stages in the lowering of the glacial 

 lakes, forerunners of the present Lake Erie. 



There are, then, three natural divisions of the Huron drainage 

 basin: (i) the loose-textured rough interlobate moraine; (2) the 

 clay morainic belt lying to the southeast of it; (3) and the low- lying 

 plain extending to Lake Erie. Each implies important differences 

 in the way of bog formation and provides edaphic factors which 

 determine to a large extent the nature of the dominant forest covering. 



PHYSIOGRAPHIC HISTORY. 



The history of these topographic features is for the most part 

 bound up with the retreat of the ice at the close of the last (Wisconsin) 

 glacial epoch. A topographic map of the region lying between Lakes 

 Michigan and Erie shows that the morainic hills so characteristic 

 of the Huron basin are part of a belt of similar physiography extending 

 from northern Indiana well up into the " thumb" of lower Michigan 

 (fig. 2). This belt of glacial deposits is directly connected with the 



