304 Tertiary. 



having little tenacity, falls in slides and avalanches into the water, and 

 is thus cut into deep, narrow gullies b}^ rains. Its surface in the above 

 district is not more than 250 feet above the lake, sloping gradually 

 from the mountains to the shore, as though it formed, at one time, the 

 bed of an ancient sea. On the waters of the St. Louis river on the 

 west, and the Ontonagon on the east, however, the red clay deposits 

 reach to the height of 450 to 500 feet above the lake. 



On the " Isle aux Barques" the lime is so abundant in the clay, that 

 it has formed in amorphous concretions throughout the mass. A few 

 leaves and decayed sticks have been seen in the red marl}' clays, 

 with carbonaceous matter and lignite, but such occurrences are rare. 

 Along the coast there are interstratified beds of sand and gravel of a 

 local character. In the interior, where the clay is visible in bold 

 bluffs, along the water courses, it is more uniform and less inter- 

 calated with coarse drift. It rests not only on the sedimentary 

 unaltered rocks, but also on trap and metamorphic and igneous rocks. 



The mass of the hills between Chegwomigon bay and the Brule river, 

 is gravel and bowlder drift. It is not very uniform iu composition, and 

 is marked by the violent action of water. The central part of this 

 peninsula presents large tracts of barren, water-washed land, and mod- 

 erately coarse gravel. Both the western and eastern knobs and ridges 

 are of coarse materials; and toward the point or extremity about the 

 "detour," and the adjacent islands, the saud and bowlder deposits are 

 represented. 



A section of three miles from the coast to the mountains, four miles 

 southwest of LaPointe, showed red marly clay 95 to 130 feet above the 

 lake, capped by coarse bowlder drift, the top of which is 428 to 509 

 feet above the lake. This drift is disposed in three very abrupt and 

 well defined terraces. These terraces continue southward around the 

 southern extremity of the mountain, and have the appearance of 

 ancient beaches or shores. 



In 1855, Prof G. C. Swallow* found a fine, .pulverulent, absolutely 

 stratified mass of light, grayish buff', silicious and slightly indurated 

 marl, capping nearly all the bluffs of the Missouri and Mississippi 

 within that State, for which he proposed the name Bluff formation. 

 The Bluff above St. Joseph exhibits an exposure 140 feet thick. 

 It is easily penetrated by the roots of trees, which decay and leave en- 

 crusting tubes, giviug it a peculiar perforated appearance. It extends 

 from Council Bluffs to St. Louis, and below to the mouth of the Ohio. 



* Geo. Sur. of Missouri. 



