syenite, I must premise that I have not found in Sky any indication to denote the relative order of the two. If indeed they are both irregular substances, as I think there is no reason to doubt, any priority or posteriority is out of the question, or at least it cannot be ascertained by examining their juxtapositions. If the one set were proved to be constantly superior to one set of stratified rocks, and the other to a different and later set, the question of rank might be settled between them: but these connections are difficult to ascertain to a sufficient extent, and possibly none such exist. If one stratified rock is in one place superior to another, we are sure that it is every where superior; but if we have ever so clearly proved that a body of trap or of any other unstratified rock is superior and in contact in one place to any given stratum, we have no certainty that it is equally so every where. Thus I shall in this island show that the trap rests in one place on the latest sandstone, in another on the earliest. No means therefore are offered here of determining the relative order of these two unstratified rocks, but I have little doubt from the phenomena which I have witnessed in Rum and Mull, that they are both portions of one irregular mass. I shall therefore commence with the trap as the most extensive.
I was once inclined to make a distinction between the trap which forms so large a part of the Cuchullin hills, and that which is found
