APPENDIX. 539 



5. Suggestions respecting the Geological Epoch of the Deposit of Sand- 

 stone Rock at St. Mary's Falls. By Henry K. Schoolcraft. 



Lake Superior presents to tlie eye the singular spectacle of a 

 body of pure translucent water, five hundred miles in length 

 from east to west, and one hundred and eighty or two hundred 

 miles wide. This vast mass of water is thought to have an ex- 

 treme depth — I know not on what principles — of nine hundred 

 feet deep. It lies at an elevation of six hundred feet above the 

 Atlantic ocean, at high water. 



From this depth there has been protruded from its bottom two 

 species of formations, which were thus elevated by volcanic forces, 

 namely, the trap and the granitical series. Cones and high mural 

 cliffs, with large rents, make this basis one of great inequalities. 

 To fill up these, the sedimentary rocks, by a natural law of gravita- 

 tion, let fall the dissolved and suspended matter which constitutes 

 the horizontal strata, such as the neutral and deep-colored sand- 

 stones. This process also gives origin to grauwackes and the 

 grauwacke slates and the argillites. But these horizontal deposits 

 do not all retain their horizon tality. They were tilted up by other 

 volcanic forces, after the deposition and hardening of the sand- 

 stones, as we see them at the north foot of the Porcupine Mount- 

 ains and along the rugged valley of the St. Louis Eiver. 



This secondary upheaval or series of upheavals, is conceived to 

 furnish proof of epochs. Strata of the same mineral constitution 

 and system of formation which are upheaved, are clearly of pos- 

 terior age to the horizontal. Some of these strata of the second- 

 ary epoch have only had their horizontality disturbed, while 

 others are quite vertical. Yet, the disturbances of an epoch are 

 only relative, and it remains true that any disturbance, however 

 slight, in the fundamental series, throws the epoch beyond the 

 newer fletz and tertiary formations. 



Some theory of this kind is necessary in scrutinizing the posi- 

 tion of the St. Mary's sandstone, which is manifestly of the palao- 

 zoic era. It has felt the impulse of disturbance, although it ap- 

 pears to be little. Evidences of this are most perceptible in the 

 British Channel, on the north side of the Island of St. Joseph. 



