. GEOLOGY. II YPERSTIIENE ROCK. 385 



for the igneous theory of this rock, that every mass or 

 vein should have originated in the former manner. 



Although the same perfect exposure cannot be obtained, 

 there is reason to think that the trap of Strathaird is 

 similar to this, and is equally the origin of the numerous 

 veins which there intersect the strata. 



There is also some reason for supposing that these 

 masses are of more recent origin than those which form 

 the bulk of the island, since the latter do not send forth 

 any such veins, but are on the contrary intersected by 

 veins of a date more recent than themselves. These 

 probably originate in masses now removed, or concealed 

 from view ; and as such masses must necessarily, like the 

 veins, be of later date than the rocks in question, it is 

 a natural consequence that there are in Sky two distinct 

 formations of trap. It is not improbable that the rock of 

 Swishnish and Strathaird belongs to the second of these; 

 a question which can only be decided when the veins of 

 Strathaird that intersect the stratified rocks shall also be 

 traced into the rock of Blaven or the other neighbouring 

 mountains. Such a connexion may accidentally be dis- 

 covered, but the nature of the country is such as scarcely 

 to admit of a regular investigation of this point. 



I have remarked in the general description that the 

 Cuchullin mountains are principally formed of a compound 

 to which I have given the name of hypersthene rock. For 

 the sake of the topography it would have been desirable 

 to define the region occupied by this rock ; although it is 

 of little consequence in a geological view, since its rela- 

 tions are not required for the purpose of comparing strata 

 or ascertaining their connexions, as if it were a stratified 

 substance : it is little more than a question respecting 

 the proportions of one or of another member of the trap 

 family. 



The difficulty of ascertaining its extent arises from the 

 thoroughly inaccessible nature of the eastern declivity 

 of this ridge, and from the almost insuperable obstacles 



VOL. i. c c 



