DEAINAGE. 335 



general , strike. Deposits of glacial sand and gravels are very abundant 

 within this valley, and for these the river often swings aside across the strike 

 for a mile or more. In sees. 21 and 29, T. 45 N., R. 31 W., and in sec. 10, 

 T. 44 N., R. 31 W., excellent rock sections are afforded by such digressions. 



The old valley between the two Archean ovals west of the Republic 

 tongue (see PI. Ill) is on the south entirely filled with glacial gravels to 

 the level of the old divides, and the large brook known as the east branch 

 of the Fence is diverted to the till-covered western of the two Ai-chean 

 ovals. The valley is clearly indicated, however, by an interesting series of 

 lakes, of which Squaw, Trout, and Sundog, each about 1 mile in length, 

 are the most considerable. 



The area drained by the Sturgeon lies in the extreme southeastern part 

 of the district, wholly within the marginal fringe of sandstone. The rela- 

 tion of its course to the geology is known in detail only within portions of 

 the Felch Mountain range. This it first enters in the northern portions of 

 sees. 35 and 36, T. 42 N., R. 30 W., in a loop into the Algonkian, from the 

 northern Archean margin, to which it again returns. Five miles farther 

 east it crosses the trough from north to south, transverse to the strike of the 

 Algonkian formations, to the contact with the southern Archean mass. It 

 follows this contact eastward for 2 miles, and then strikes southward across 

 the Archean to the Menominee River, not again returning to the Felch 

 Mountain range. The river valley in the Felch Mountain range is very 

 distinct, and where bordered by Potsdam outliers is rather deep, with pre- 

 cipitous banks. It is but slightly affected by drift deposits. Its course 

 shows an almost complete disregard of the structure of the Algonkian and 

 Archean rocks, and so has the usual characters of a superimposed stream. 



The Michigamme River, as was early noted by Pumpelly, has practically 

 no eastern bi'anches within this district. The Escanaba and Ford rivers, 

 which reach Lake Michigan directly, and the Sturgeon, which joins the 

 Menominee below the mouth of the Michigamme, all head within 2 or 3 

 miles of the latter, the course of which is transverse to their general direc- 

 tion. The Michigamme thus flows along the eastern edge of its drainage 

 basin. This fact — the most striking in the general distribution of the streams 

 of the district — is the result of causes which, in part at least, go back to very 

 remote geological periods. 



