28 Dr. Mac Culloch*s Sketch of the 



I shall now proceed to consider the nature of the rocks which 

 compose this island, in as regular a detail as my opportunities and 

 its intricate and unsettled geography allowed me to observe and 

 record them. 



It was not without repeated efforts and much careful tracing of 

 the successions of the stratified rocks through coasts difficult in them- 

 selves and far distant from each other, that I was able to discover the 

 key to the very great obscurity in which these are involved. It will 

 be seen that there are yet points unexplained, particularly respect- 

 ing the trap rocks, a circumstance which will not surprise geologists 

 who know that to patience, toil, and good seasons, must often ba 

 superadded good fortune ; the casual discovery of perhaps the only 

 point over a wide tract which is capable of yielding the explanation, 

 of which we are in pursuit. 



As the mica slate and its associate the quartz rock are the most 

 ancient of those which I have ascertained in Sky, I shall com- 

 anence from them as the foundation of the whole structure. I 

 have associated these rocks in this manner, because I have generally 

 found them, alternating, and bearing a common relation both to 

 those which appear to hold a deeper, and to those which have a 

 more superficial position with regard to them, the granite and the 

 stratified rocks ; but I need not repeat these reasons here as I have 

 discussed them at sufficient length in the account which I formerly 

 gave of quartz rock.. I have not however traced any decided alter- 

 nation between these two rocks in this island, nor, as far as I have 

 observed, is it likely that any alternation will easily be traced, since 

 the beds of both are far less regular than is usual when they are as- 

 sociated in an alternating ordeu The mica slate is found occupying 

 the district of Skat, and it extends from the point of that promon- 

 tory to an irregular line drawn between Loch Eishort and LocK 



