Mineralogy of Sky, 77 



It follows then that the syenite is posterior to the trap veins, and a 

 further confirmation of this is found near Scavig, where a set of trap 

 veins is also to be seen which traverses the red sandstone, but does not 

 pass through the incumbent trap; therefore the syenite, and the moun- 

 tain trap of the Cuchullin, are each posterior to one set of trap veins. 

 This adds a probability to my conjecture, that the mountain trap and 

 the syenite are of one period ; it cannot be said to prove it because we 

 have no means of knowing whether or not these separate sets of veins 

 belong to one period or to more. Community of structure proves 

 nothing in this case ; they are equally formed either of a coarse basal- 

 tic substance, which can scarcely in strictness be called basalt, or of 

 porphyritic trap ; and would be with still less propriety denominated 

 greenstone, since the two substances, whose distinct union forms this 

 latter rock, and whose imperceptible mixture is supposed to form the 

 other, cannot be traced in it. 



But I must not terminate the history of these veins which appear 

 in such a profusion of intersections in the vicinity of Scavig, without 

 remarking that however numerous they may be, and consequently 

 however large the space which they occupy, they produce little or 

 no disturbance in the regularity of the sandstone beds which they 

 traverse, nor does that rock appear to undergo any alteration in 

 their vicinity. This remark will appear the more necessary hereafter, 

 when I shall describe a similar but infinitely more striking pheno- 

 menon at Strathaird. 



There is a second set of veins however, which traverse not only 

 the mountain trap but the veins first named, and which are clearly 

 of a posterior date. These are much smaller, often indeed not ex- 

 ceeding half an inch in breadth, and are composed of an extremely 

 fine and hard black basalt. They are less abundant than the first 

 where even they exist, and they are not found in nearly so many 



