278 Dr. Mac CuLLOCH o« the Geology of Glen Tilt, 



alternating. These veins originate in the mass of granite which 

 forms the mountain, and this observation is important, as I shall 

 hereafter shew that the granite seen in the Criny is a portion of 

 the great central granite mass which forms the whole range of hills 

 on the right bank of the Tilt. 



From Glen Criny a succession of schist and quartz rock is to be 

 observed, extending till within a few hundred yards of Gow's 

 bridge ; but the bed of the river being here inaccessible, we can 

 only obtain a general view of it. The last bed of quartz rock in 

 this direction is immediately followed by a bed of limestone, and 

 this again is succeeded by an alternation of beds of schist, lime- 

 stone, and quartz rock for some hundred yards below that bridge, 

 together with masses of porphyry both of a reddish and a greyish 

 colour, but whether disposed In beds or veins I have been unable to 

 ascertain, though I Imagine that they are beds, since they seem to 

 conform to the stratified rocks. As this collective mass presents 

 some Interesting circumstances It will require a more minute de- 

 tail. 



The position of the whole of these beds Is regular, with two 

 very slight exceptions, and they occupy a space extending from 320 

 yards or thereabouts above Gow's bridge to 200 below it. 



We have seen that all the irregularities of the beds take place 

 wherever the granite comes into contact with thera. Here there is 

 no granite present, but, on the contrary, the mass of limestone of 

 which these beds form a part, and which has hitherto been found 

 terminating In the bed of the river, is continued to the right hand 

 ridge, and may be traced high up in the hill, where the contact with 

 the granite takes place.* The only exception with regard to the 



* Vide Section, Plate 20. fig. 1 . 



