300 Tertiary. 



posed of fragments of the rocks in situ, showing that, whatever may 

 have been its origin, it could not have been acted upon by long con- 

 tinued agencies. A few foreign pebbles exist in it, generally trap, and 

 evidently derived from the neighborhood. Greatest thickness 30 feet. 



2d. Drift clay, or red clay. It is a mixture of loam and clay, and 

 its color is owing to the decomposition of the red sandstone and trap 

 from which it has been derived. It is mainly composed of very finely 

 comminuted substances, yet there are pebbles interpersed through it, and 

 even bowlders of considerable size, general!}^ rounded and smoothed. 

 Fragments of metallic ores and native copper occur occasionally in it — 

 the latter sometimes weighing several hundred pounds. It is found 

 along the whole southern coast of lake Superior, resting upon the red 

 sandstone, and limited to a certain height, but on the Ontonagon and 

 Carp rivers, it is found in depressions on elevated lands, 500 feet above 

 the lake. At Grand Sable where its base rests on almost horizontal 

 strata of red sandstone, a few feet above tlie water, and its top is 

 covered by a mass of drift sand, it is 60 feet in thickness, and ex- 

 hibits lines of stratification disposed with great regularity. 



3d. Drift sand and gravel. This is the most widely difl^'used of the 

 drift deposits on the shores of lake Superior and the northern part of 

 Michigan. The greatest thickness observed is at Grand Sable, where 

 it is 300 feet thick. 



4th. Bowlders. These occur of every size and description in great 

 numbers along the whole southern shore. The largest noticed being 

 of hornblende, and measuring 15 feet in length, 11 in width, and 6^ in 

 height. The bowlders have been moved from north to south, but have 

 not come from far, though some of them have been transported from 

 the north shore. It is noticed among the ridges north of Carp river, 

 that the valleys, for the most part, contain bowlders from the next 

 ridge to the north ; and there are instances where a ridge did not al]o^\ 

 the fragments of the preceding ridge to pass. This limitation pre- 

 vails only within the hilly portion of the Lake Superior region between 

 the lake shore and the dividing ridge. South of this ridge no barrier 

 occurs. 



5th. Drift terraces and ridges. These may be seen both on the 

 north and the south sides of Lake Superior, but the}^ ^ire less striking 

 than around Lakes Erie and Ontario. The}^ are most conspicuous on 

 the south shore, between Saut and Keweenaw point. Their average 

 height is about 100 feet. At a place two miles east of Two-hearted 

 river, the following succession occurs : gravel beach, 5 feet ; sand 



