OVERLYING ROCKS. 469 



eluding stratified rock, or sends ramifications 

 through the whole series. 



But there is one case in which these rocks 

 seem to form strata unconnected with veins, and 

 absolutely parallel ; and, of this, the north-western 

 coast of Sky presents examples, as the north- 

 eastern does of most of the other circumstances 

 here detailed. These strata alternate with jasper, 

 siliceous schist, and ferruginous clay ; probably 

 also, with chert or indurated limestone. It will 

 hereafter be shown, that shale is convertible, in 

 similar circumstances, into siliceous schist, a sub- 

 stance strongly resembling basalt ; and it is easy 

 therefore to account for these strata, by suppos- 

 ing that, from the same cause, such substances 

 have been converted into those strata of trap of 

 various kinds, which their several peculiarities of 

 composition enabled them to assume. 



In a few cases, where deep sections of cliffs 

 afford opportunity for examination, it is also 

 found that irregular masses lie beneath the stra- 

 tified rocks in some places, just as they surmount 

 them in others ; and that, from these also, veins 

 proceed to the surface, or in other directions. 



