Granite of Aberdeenshire. 45 



it must lie on the primary strata alone, and not on the secondary, 

 and thus also it might exist in masses intermediate between 

 these two classes of stratified rocks. We are by no means 

 sufficiently acquainted as yet with the multitude of existing 

 appearances to pronounce a negative on this subject ; and the 

 difficulty of investigating accurately phenomena of a much 

 more obvious and simple nature, will teach experienced geo- 

 logists to reserve their opinions respecting it for a period of 

 greater information. 



It has moreover been shewn in this paper, that greenstone 

 and basalt, or rocks identical with these in their mineral cha- 

 racters, occur as varieties of the most decided granite ; and it 

 must also be well known to all observers, that the limits be- 

 tween granite and some of the porphyries connected with it, 

 are frequently evanescent. It is therefore far from improbable 

 that some of the superincumbent masses of these substances 

 which are found on the primary strata, are truly connected with 

 subjacent granites, and are modifications of that rock, not of 

 those of the more recent trap family. 



Having thus stated the geological resemblance which exists 

 between granite and the trap rocks, and having, in the preceding 

 part of this paper, pointed out the identity in mineral character 

 between certain varieties of granite and others appertaining to 

 the latter family, it remains to enumerate some of the most 

 remarkable instances in which the trap rocks assume those 

 characters which are predominant, and have been esteemed 

 essential, in granite. 



In the island of Sky there is found a body of primary strata, 

 succeeded by a tract of secondary limestone, shale, and sand- 

 stone. This secondary tract is, throughout the greater part 

 of its extent, covered by an immense mass of trap rocks, the 

 proofs of their superincumbent position being displayed very 

 distinctly in many places. Most of the varieties of this family 

 which are as yet known, and one which exists only here and 

 in the neighbouring land of Airdnamurchan occur in this space, 

 and the whole of them are connected by imperceptible gradations. 



