Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/59

 complete, and consequently the same for the whole way upwards. Now in our system of geology, not only is this sandstone considered the first of the secondary strata, but the schistose rock is ranked among the primary or among the transition; and the difficulty will be equal which ever term we adopt. If the nature of the sandstone did not determine its rank, its place after the schistose rock would be sufficient for that purpose: so that here the primary and secondary strata are not only following in conformable order, but that order is demonstrably not accidental as in Mull, where an instance of this nature occurs, since there is a perfect interference and alternation of the two at the point of contact. Those rules therefore, which would define the secondary rocks by their want of conformity to the primary, either have not selected the first of these primary rocks as their basis, or, the law of non-conformity and of a thorough separation between the two classes is exceptionable.

Having thus as far as is in my power described, according to their superposition, the rocks which seem to follow in the most regular order, I shall proceed to describe those which are uppermost, the trap and syenite, which will complete the account of the rocks of this island. In naming these as uppermost, I am far from meaning to say that they are exclusively so, as I shall on the contrary show that they also penetrate the superior strata. No distinct position can in fact be assigned to rocks which are not stratified, and such are generally granite and trap. These unstratified substances interfere with almost all the regularly placed rocks. Although granite is not indeed found passing through or lying near the primary stratified rocks, unless in the form of veins, yet it bears no regular relation to them, and is occasionally found in the same place, in contact with every individual of a series of different stratified substances. The other unstratified rocks, trap and syenite, bear a still more intricate relation