Mineralogy of Sky » 79 



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 re- 

 specting 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 inter- 

 esting features in themselves, and are of no evidence in geological in- 

 duction, and finish by describing those that are to be seen at Stra- 

 thaird, which are well worthy of notice on account of their extraor- 

 dinary 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.* 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 di- 



* See PI. 4. fig. 3. 



