STATE GEOLOGIST. 131 



The bed is traceable along the shore for a quarter of a mile, 

 but nothing more is known of its extent. A single fragment 

 was seen on the opposite shore of the bay. 



The bed E, above the lignite, has evidently been deposited, by 

 the action of fresh water, since the epoch of the lignite; while 

 the bed B, beneath the lignite, may belong to the same or may 

 represent the glacial or boulder epoch. 



Several other lignite beds are known upon the shore, of Lake 

 Superior, and I am informed J;h at the ii<habitants of that regioji 

 are beginning to learn their use. 



The inequalities left in the surface of the assorted drift, upon 

 the withdrawal of the submerging ocean, remained filled with 

 w,ater, which, by constant drainage to the sea, in connection 

 with accessions of fresh water only, have become our numerous 

 inland lakes. These for many ages have been gradually filling 

 up from several sources. 1st. Rains have transported the finer 

 materials from the surrounding hills into these little basins. 

 2d. Spring-waters, charged with calcareous matter, have not 

 only supplied the lakes with that material, but. have precipitated 

 large amounts upon the bottom. 3d. Mingled with these cal- 

 careous sediments, the dead shells of fresh water molluscs have 

 accumulated in very great abundance. , The union of these_; 

 calcareous materials has formed a deposite of marl, continually 

 thickening. 



Around the shallow margins of these lakes is always a belt, 

 abounding in various forms of aquatic vegetation, which, de- 

 caying, form a deposite of vegetable matters, resting upon the 

 marl, from the water's edge to the, inner limit of vegetable 

 growth. With the filling of the interior, the shallow belt 

 extends toward the center, and the vegetable deposite .contin-. 

 ually encroaches upon the lacustrine area, until the whole lake 

 becomes a peaty marsh, with a bed of marl at bottom. Subser 

 quent accessions of vegetable and calcareous matters fill the 

 interstices of the porous soil, exclude the standing water,, and 

 convert the reeking^ marshj into dry and arable land. We 



