192 Dr. MacCulloch's Supplement to the Mineralogy of Sky. 



occur in the lateral action of rivers on the alluvia of vallies ; on the 

 banks of the Tay and in many others of the principal rivers of 

 Scotland. Greater effects have often been attributed to the corrosive 

 powers of the sea, and in indulging this speculation I have kept far 

 within the range commonly occupied by geologists. I may remark 

 that the narrowness of the channel, which in one part does not 

 exceed a quarter of a mile, and the shallowness of the soundings 

 compared with the depth of those which separate the other parts of 

 Sky from the main land, are friendly to this supposition. These 

 scarcely exceed ten fathoms in the middle, although there are some 

 deeper holes on each side ranging to thirteen, the bottom being 

 every where gravelly, as if, like the banks, it was the remains of 

 some former alluvium. 



