Mineralogy of Sky, 51 



complete, and consequently the same for the whole way upwards. 

 Now in our system of geology, not only is this sandstone con- 

 sidered the first of the secondary strata, but the schistose rock is 

 ranked among the primary or among the trafisition; 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 th« 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 ev^ry indivi- 

 dual of a series of different stratili:^d substances. The other un- 

 stratified rocks, trap and syenite, bear a still more intricate relation 



G 2 



