ON THE SOUTH SHORE OF LAKE SUPERIO E. 



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be made of the rapidity of this sedimentary action from the case of the schooner 

 Acorn, which was sunk off Cleveland, in Lake Erie, in sixty-eight feet of water, in 

 the fall of 1843. She was two months in the water, and had upon her deck when 

 raised one-fourth of an inch of mud. Lake Erie has about its western half a deposit 

 of blue marly clay, upon which water acts rapidly ; and here, as on Lake Superior, 

 the water after storms is rendered turbid for several miles out. 



b. Gravel and Boulder Drift. — The mass of the hills between Chegwomigon Bay 

 and the Brule River, is a recent drift. It is not very uniform in composition, but 

 always marked by violent action of water. The central part of this peninsula pre- 

 sents large tracts of barren, water-washed land, and moderately coarse gravel. Both 

 the western and eastern knobs and ridges are of coarse materials ; and towards the 

 point or extremity about the " Detour" and the adjacent islands, the sand and 

 boulder matter is found, as represented in the sections, interstratified with red clay. 

 Wherever we descend to the level of one hundred to two hundred and fifty feet 

 above the Lake, the red clay is met with, extending from the shore along the 

 valleys towards the interior, like bays indenting a coast. This drift formation is 

 chiefly remarkable for its great elevation and its prodigious mass. 



In the region in rear of the Penokie Range, it occupies a large tract, concealing 

 the rocks to a great depth, rising eight hundred to one thousand feet above the 

 lake-level. 



The Sedimentary and Igneous Rocks. — The relative age of the rocks beneath the 

 clay and drift is a subject upon which a prolonged discussion would be in place if 

 theoretical considerations might be introduced here at large. The granites and 

 syenites of the interior are no doubt the most ancient rocks of the District. After 

 the protrusion of those extensive, interior granitic masses, many successive changes 

 have occurred, but in what precise order is a question not easily determined. The 

 immense sandstone deposits of the basin of Lake Superior must have been subse- 

 quent to the granites of Wisconsin, Chippewa, and Montreal Rivers, and probably 

 rested on them. Since that era, a prolonged and intense internal igneous action 

 has taken place, and the trap, hornblendic, and greenstone masses have been ejected, 

 and also with them irregular protrusions of recent granite and syenite. The meta- 

 morphic slates have been elevated during these convulsions, and the sedimentary 

 rocks thrust away to the northward, and tilted up at high angles. 



The old granites and syenites have been rent, and fluid matter, such as quartz 

 and hornblende, inserted in the fissures and between the beds. Along the northern 

 portion of the Penokie Range an outburst has taken place, as it were between the 

 sedimentary rocks and their ancient basis, on a line from the Montreal to Lac 

 des Anglais ; but the overflows have not been confined to one volcanic effort. The 

 black and red trap, against which, the conglomerate abuts, is doubtless due to a, 

 different effort from that which produced the greenstone trap-rocks, that rise between 

 the East Fork of Bad River and the Montreal. The augitic, hornblendic, and 

 syenitic mountains between the East Fork and the main stream, differ in form, in 



