ON T H E 



NORTHWEST 



S H 0 R E OF LAKE SUPERIOR. 



389 



to the action of gas permeating the rocks from below, but I am inclined to attribute 

 it to the action of water. The same phenomenon occurs at many other places on 

 the lake-shore, but it has not been observed at any point inland where similar rocks 

 occur in situations removed from the constant action of water. About the centre 

 of the chain, which encloses the bay on the lake-side, the rocks are polished and 

 excavated, to the depth of four or five feet and the width of ten or twelve. This 

 great gutter is literally covered with small parallel grooves and scratches, and 

 extends the whole length of the exposure. The rock is an exceedingly inde- 

 structible one, and there is not a groove or scratch in the direction which masses 

 of ice, moved by the present waters of the Lake, would be compelled to take. 



The entrance to the bay is through a narrow gap in the rock just described, with 

 barely water sufficient to permit a Mackinaw boat to pass. The bay, which is 

 sheltered from every wind, is situated between two ridges, about six hundred yards 

 apart, bearing east and west; and its peculiar shape is given it by a north-30°-east 

 dike, which shows itself at the extreme eastern end of the first ridge, and forms the 

 barrier between Bitobigungk and the great bay below, and two other dikes with the 

 same bearing, which are seen low down in the next bay. The trough between the 

 east and west ridges, as seen at other points, contains a thick deposit of soft shales, 

 and in them the basin of the bay has been excavated. 



In describing the rocks on the lake-shore between Bitobigungk Bay and Wisa- 

 code River, I shall begin at the last-named place and proceed westerly. 



In the bay immediately above the mouth of the Wisacode, are several low expo- 

 sures of metamorphosed clay-slates (No. 73), associated with a basaltic bed (No. 

 72). The joints of the altered slates present a remarkable appearance, having 

 been filled, apparently, with melted matter of the same rock. No. 73 continues 

 along the shore, past the small rock-islands, as far as the deep bay into which 

 Diarrhoea River empties. It is in low exposures, at the points separating the bays, 

 and occasionally projects from beneath the sands of the beach. At one locality, it 

 is overlaid by a bed of trap. In the bottom of the bay there is a greenstone dike 

 (No. 74), twenty-six feet wide, and bearing east 10° north. At the junction of the 

 dike with the sedimentary rock, large cells are developed in the latter (No. 75), 

 which contain laumonite and other zeolites. The joints of the trap are encrusted 

 with heulandite. The first range of hills along this part of the coast, are from two 

 and a half to three miles back from the shore, and bear northeast and southwest. 



Near the west end of the bay the altered slate dips southeast 14°. At the 

 point it is overlaid by a bed of trap. At the point opposite the large island, No. 

 638 is the overlying rock. It contains many portions of a very hard trap, 

 numerous thin veins of quartz, and many egg-shaped cavities filled with the same 

 mineral, the quartz being surrounded with a coating of chalcedony. A narrow 

 dike, bearing north and south, traverses the bedded rocks at this place. Just above 

 the point is an exposure of amygdaloid, with beds of altered sandstone (No. 76) 

 above it, and over them a bed of trap. Some portions of the exposure are earthy- 

 looking, while other parts present every appearance of having been fused. A short 

 distance above this place, the beds consist of metamorphosed sandstone, shale, and 

 seams of clay, as illustrated in the following section : 



