SKY. GEOLOGY. SECONDARY STRATA. 351 



There is consequently sufficient evidence of the identity 

 of the hard and soft strata, and therefore of the original 

 continuity of those of Strathaird with those which now lie 

 at Swishnish separated by the breadth of the loch. Omit- 

 ting the character of hardness, there is a striking similarity 

 between these different strata ; the same varieties in colour 

 and composition occurring both in the soft and in the hard ; 

 the grains of sand also that form the body of the rock being 

 in the one case loosely aggregated and separated by 

 calcareous matter, in the other condensed almost to the 

 state of quartz, and in some instances converted into a 

 cherty substance by a combination with the lime. It 

 is needless here to dwell on the obvious explanation of 

 these changes which the presence of the trap offers ; 

 since it is so nearly connected with many analogous 

 phenomena that will be described in other parts of this 

 work. 



With these strata the description of the regular rocks 

 of Sky terminates ; but it will not be useless to bring 

 under review the connexions of the whole, for the purpose 

 of examining the analogy which they bear to similar 

 rocks occurring in other situations. This is rendered 

 the more necessary by the numerous irregularities they 

 present; by which their natural order is so far obscured 

 as to add materially to the labour of the geologist, 

 and to interrupt equally that consistency of description 

 with which their history might otherwise have been given. 

 These increase nevertheless the interest of the phenomena ; 

 presenting at the same time a valuable set of facts for 

 explaining analogous derangements of a less obvious 

 nature, and affording useful lessons to the geologist 

 who may engage in similar investigations. 



It has been shown that the position of the gneiss is 

 regular, and that under peculiar modifications it is followed 

 by a series of sandstone, equally regular, of which the 

 members are, with trifling exceptions, similar or analogous 

 throughout, and persistent across the whole island. These 



