202 



TRANSACTIONS OF THE 



part covered with soil and therefore are capable of sus- 

 taining vegetation; whereas the gorge presents all the 

 characters of a fissure whose faces are chiefly covered 

 with a talus of naked rock fragments. 



Had a gradual wearing down, or hollowing out, of the 

 ravine taken place, there would necessarily have been 

 a corresponding slow reduction in the level of the lake, 

 which the circumstance of a single strongly defined 

 beach line negatives. 



So decided is the character of this bench in agreeing 

 with the wave- worn margin of a lake, that a carriage 

 road from Lewistown has actually for some time been 

 conducted over the mountain, its projectors having 

 availed themselves of this favourable natural feature, to 

 pass for many miles westward along this elevated bench. 

 It must be admitted that no remarkable comminution of 

 rocks, or distribution of rolled pebbles, as upon the sur- 

 face of a long worn beach, can be observed ; nor can 

 it be expected, in a position where the detritus of the 

 ridge is constantly descending upon its surface, from an 

 elevation of three hundred feet. For the most part the 

 surface stones are of moderate size, and occasionally sand 

 prevails. 



I am inclined to attribute the sudden drainage of this 

 lake to a fracture or fissure of its margin; occurring 

 transversely to the direction of the ridge, and occasioned 

 by some such power as an earthquake, or by one of the 

 many causes of contraction, subsidence and final disrup- 

 tion, in the previous arrangement of the subjacent rocks. 

 Perhaps this fracture may have extended much farther 

 than simply as exhibited in Jack's mountain, as some- 

 thing like corresponding and continuous depressions, on 

 a smaller scale, are observable for several miles, both to 

 the south and the north, in the same line. When once 

 a fracture or fissure had been made across the barrier 

 the pressure of a hundred square miles of water several 



