ON THE NORTHWEST SHORE 



OF LAKE 



SUPERIOR. 



409 



the most dreary and desolate imaginable. In the distance of four hundred yards, 

 the river falls one hundred and forty-four feet. The fall is in a series of cascades 

 through a narrow gorge, with perpendicular walls, varying from forty to one hun- 

 dred and twenty feet in height, on both sides of the river. The gorge is from fifteen 

 to thirty feet in width, and crooked, presenting numerous angles, around which the 

 foaming waters fret their way with arrowy swiftness, plunging down abrupt slopes, 

 or falling in beautiful cascades. 



The slate, of which there is a fine exposure here, dips south-southeast, at an 

 angle of 8° ; and including the beds of the next mile above, is about two hundred 

 and fifty feet in thickness. The lower beds (No. 44) are unaltered and very fissile. 

 In the vicinity of the trap dikes, however, they are highly metamorphosed (No. 

 45). Two dikes cross the river here; one a coarse-grained hornblendic greenstone 

 (No. 46), which disintegrates easily, and bears northwest; the other a prismatic 

 dike of fine-grained greenstone, bearing north and south. The following figure 

 exhibits a section of the rocks at this place. 



a be a d 



a, a. Argillaceous slate, b. Trap dike. c. Vein of calcite. d. Prismatic dike. 



The dike, No. 46, is accompanied by a wide vein of calcite (No. 47). Where it 

 touches the water on the American side, which is about forty feet below the highest 

 exposure, it is somewhat broken. The wall-rock is trap (No. 48) on one side, and 

 slate on the other. From the bottom of the lower cascade to the top of the slates 

 at the head of the falls, the height is one hundred and fifty-nine feet. For the dis- 

 tance of three quarters of a mile above this, the river has little or no current, 

 several rapids then occur, and the stream flows between slate hills until the west 

 end of Grand Portage is gained. 



Opposite the site of old Fort Charlotte, Pigeon River is thirty yards wide, and 

 the rocks are displayed on both shores, dipping southeast at an angle of 8°. In 

 ascending the stream, the next rock exposure is at the second portage, counting- 

 Grand Portage as the first. At this place a greenstone dike, one hundred and sixty- 

 eight feet wide, crosses the river, bearing northeast and southwest, and accompanied 

 by a vein of calcite. On the northwest side, the trap disintegrates easily, and there 

 is some appearance of a breccia between it and the slate. There is a fall here of 

 forty-one feet in three perpendicular cascades. Including the rapids above, the fall 

 is fifty-five feet. Above the falls, the dip of the slate is northwest 8°. Below, is a 

 narrow gorge cut through the greenstone dike, and the slates in contact with it are 

 much altered, and the dip reversed to the southeast, at an angle of 17°. The 

 section on page 410 shows the disposition of the rocks at this place. The ridge 

 made by the dike here is the most northwesterly one in the Grand Portage range. 



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