Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/85

 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 mountain trap of the Cuchullin, are each posterior to one set of trap veins. This adds 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 basaltic 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 phenomenon 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 exceeding 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