but generally perpendicular directions. They are of a very large size, and are frequently stratified, a circumstance not uncommon in basaltic veins. They do not resemble the small ones of the second rank which I have described already.
If, as some have seemed inclined to do, we should adopt a notion that all trap veins were of the same period, the existence of these in the stratified trap, while they were absent from the mountain trap, would lead us to conclude that this latter was a posterior formation to the other. This is possible, and I have certainly no proof to the contrary. But from what I have shown respecting the certainty of two distinct sets of these veins, and the possibility of more, it is plain that they can prove nothing respecting either the difference or identity of these two rocks. If there are two sets of veins there may be three or more.
As no useful purpose is served by describing all the trap veins which abound in these countries, I shall pass over many which offer no interesting features in themselves, and are of no evidence in geological induction, and finish by describing those that are to be seen at Strathaird, which are well worthy of notice on account of their extraordinary number, and of some particular appearances by which they are distinguished. I have already slightly mentioned them in the general description of this coast: I must now be more particular, and, to give an idea of their general appearance, I have subjoined what must rather be considered as a plan than a drawing, since the formality of the subject admits of nothing else.[1]
I pointed out their
extraordinary numbers, and may now add that in consequence of
their frequency they nearly equal in some places, when collectively
measured, the stratified rock through which they pass. I have
counted 6 or 8 in the space of 50 yards, of which the collective dimensions
- ↑ See Pl. 4. fig. 3.
