OF LOCHABER. 53 



Muckul, to join the lower part of its former run. This se- 

 condary state of matters is represented in Plate VIII. fig. 2. 

 Although it is not very easy to conceive what might be the ex- 

 act effect of this change, in the course of so very considerable 

 a body of running water, yet there can be no doubt that its 

 power would in time be felt, directed, as it now came to be, 

 against a thin barrier, composed of soft materials, and already so 

 much weakened, as it must have been, by so great a rush of 

 water, as that which pressed over it during the sinking of Loch 

 Roy from the level of Shelf 2d to that of Shelf 3d. Indeed the 

 very circumstance of admitting the possibility of such a breach 

 having ever taken place once, implies that the causes for its hap- 

 pening a second time must have been greatly multiplied ; nor 

 can any one hesitate in believing, that if the destruction once 

 began, it would likewise be now proportionably much more 

 sudden and tremendous. Be it remembered, too, that althoueh 

 the perpendicular height to be swept away, was greater upon 

 this second occasion than it was in the first instance, yet it 

 was not necessarily very great, — not certainly of necessity 

 more than about two hundred feet, the difference of elevation 

 between Shelf 3d and Shelf 4th. We see, indeed, by the ap- 

 pearances remaining in Glen Collarig, where there has been 

 little or no change since that rupture, which, during the second 

 subsidence of Loch Roy, let off a portion of its waters there, 

 that the opening which took place in the barrier between the 

 Gap and it, did not extend to half that depth, otherwise the uni- 

 ted Lake of Roy and Spean would have gone entirely through 

 there, and would have made an island of the hill of Bohun- 

 tine. But where the Roy now flows on the eastern side of 

 that hill, the depth of barrier destroyed must have been at 

 least equivalent to that of the depth of Shelf 4th below the le- 

 vel of Shelf 3d. But as I shall afterwards exhibit causes for 



the 



