SKY. GEOLOGY. OVERLYING ROCKS. 379 



instances formerly enumerated, of interference with the 

 secondary rocks, these latter occupying a definite region 

 separated from them by a boundary incapable of deep 

 examination. But in many parts of Trotternish, and 

 principally on the eastern shore, abundant and most 

 interesting examples of this nature occur, exceeding in 

 number and variety all those which have been hitherto 

 enumerated in Scotland. 



The character of this trap is also different from that of 

 the western shore. In the latter tract it generally presents 

 a stratified appearance, one substance being succeeded 

 by another, sufficiently different, although of the same 

 family, to cause the line of separation to be visible even 

 from a distance. But here the appearance of stratification 

 does not take place, although the horizontal line which 

 separates the strata from the incumbent trap presents a 

 deceptive appearance of it ; while a tendency to the 

 columnar structure is every where to be seen. This 

 tendency is particularly marked at the northern ex- 

 tremity of Trotternish, as well as on its western shore, 

 and extends in a certain degree to the opposite pro- 

 montory of Vaternish. In a few cases, the most remarkable 

 of which have already been described, the columns attain 

 considerable regularity; yet they are never so perfect 

 as in Staffa, nor are they horizontally jointed as in 

 that island. In some places however the ranges are 

 distinguished by a peculiar feature, a whole series being 

 cut through by one long extended horizontal joint as 

 decided as if it had been made by a knife, while the ends 

 of all the columns above and below it, remain continuous 

 in adaptation and without any marks of displacement. 



It is unnecessary to describe the nature of all the rocks 

 over this large space, but the general aspect of them 

 is that of greenstone, varying in the fineness of the 

 admixture, and sometimes assuming the appearance of 

 basalt. Occasionally, amygdaloidal masses are also 

 found, but as no useful information could be conveyed 



