4 University of Michigan 



Sturgeon, where it cuts across both the Archean and the Algon- 

 kian rocks. This course is due to a clay moraine which Hes 

 along the east side of the Sturgeon and the East Branch of 

 that river. Several outlying patches of moraine are on the 

 western side of the river; the largest of these, w-ith an area 

 of about two square miles, is north of Brown Lake and the 

 West Branch. A sandy ridge also lies along the east side of 

 the lake itself. - 



At some past time, Brown Lake was apparently consider- 

 ably larger than at present, as a beach-line extends around it 

 and about half a mile up W'hat is now the valley of the East 

 Branch. At that time the lake appears to have emptied into 

 the East Branch. An old channel connects the East Branch 

 with the main portion of the Sturgeon to the south. This is 

 evidence that the old junction of the East and West branches 

 was about two miles below the present confluence. 



This former course of the lake and river was apparently 

 determined by a very low, rounded ridge which lay between 

 Brown Lake and the West Branch. This dammed up the 

 former lake until it rose higher than the outlet to the east; 

 then a channel was eroded across the ridge to form the strik- 

 ingly recent, short and shallow gorge, through which the 

 waters of the present lake join the West Branch to form the 

 main river. This lowered the lake to such a degree that it 

 diverted the East Branch from its old channel so that it now 

 flows into Brown Lake. 



-See Frank Leverett, 191 1, The Surface Geology of the Northern 

 Peninsula of Michigan. Mich. Gcol. Biol. Surv., Publ. 7, Geol. Series 

 5, Plate I. 



