Mineralogy of Sky. 81 



durable and compact basalt. I have given a sketch of It. (PI. % 

 fig. 3.) I may finish the description by saying that the continua- 

 tions of theje veins are to be seen between Swenish and Kilbride, 

 at least, veins similar in appearance and equally numerous, but 

 that there is no trace of them on the opposite shore of Sleat in the 

 places which their prolongations would cut : they are not therefore 

 extensive in their courses. 



It has been so general an observation that the courses of trap veins 

 are attended with disturbances cf the accompanying strata, that it 

 seems almost to have passed into a rule among geologists. 

 The present instance is a most remarkable one to the contrary. 

 Although they are here so numerous, not the slightest disturbance 

 takes place in the evenness and the horizontality of the strata of 

 sandstone which they intersect. There is neither contortion, bend- 

 ing, fracture, or displacement, nor do they appear to have affected 

 the texture of the rock, since it is the same both at the place of con- 

 tact and at a distance from it. Of exceptions to general rules it is 

 rare to meet with any so pointed and so strong ; and though there 

 is no room for any long commentary on it, I cannot entirely quit 

 this very remarkable place without pointing out one extraordinary 

 effect which must have resulted from the intrusion of these veins. 

 If the lateral dimension of the collective veins is assumed at one 

 tenth of that of the stratified rock, (and I have reason to think this 

 estimate not excessive) it is platn that the stratified rock of Strathaird 

 must have undergone a lateral extension equal to that quantity ; a 

 motion so great that it is extremely difficult to reconcile it with the 

 present apparent repose and regularity of the whole. 



Vol. III. 



