Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/191

 plain that the appearance of stratification in the trap is here the result of the form of the rocks on which it is placed, or among which it has intruded, in the former case surmounting them, and in the latter appearing to alternate with them. The instances of this apparent alternation are highly interesting, from their great extent, as well as from the perfect conviction which they present of the fallacious nature of this supposed connection. In many cases the alternations of the trap are as regular, as decided, and as evenly parallel, as those of the stratified rocks themselves, the sandstone and limestone among which it lies. Yet in no instance does it not happen, but that at some point or other the alternating bed of trap will detach an intersecting vein, unite itself to the superincumbent mass, or, quitting the interval between two given beds of limestone or sandstone, make its way across the one immediately above or below, and then proceed with a regularity as great, for another long space, between some other pair of proximate strata. In one or more instances I have observed this to happen after more than a mile in extent, throughout all which space not the minutest irregularity had appeared to indicate any thing else than a perfectly conformable and alternating stratification. I have no doubt that, could such extensive exposure be oftener procured, all the instances of supposed alternation between the trap rocks and the stratified ones would prove similar to these.

With respect to the trap itself it is most generally amorphous. As we approach however towards the northern end of the promontory it becomes columnar, and this character prevails round the points of Aird and Hunish beyond Duntulm, where it at length terminates. Although the columns are formed on a large scale, and are individually rude and imperfectly defined, yet their picturesque effect, when seen from a point of view where they can be properly comprehended