Dr. Mac Culloch on the Geology of Glen Tilt. 26? 



the larger masses of granite with the same ease as when they traverse 

 the schist : in others, however, they appear both to originate and end 

 in the limestone, and present rather the aspect of detached lumps and 

 irregular processes than of veins.* So confused is this interference, 

 that a fragment of granite is often found entangled in the lime- 

 stone, and a lump of the latter will sometimes be found intruding 

 kito the former. The minuter veins of granite are generally if 

 not always connected with the larger pieces, and they intersect and 

 reticulate the whole limestone as they do the schist, diminishing at 

 length to the thickness of a leaf of paper or a thread. But there is 

 a still more remarkable arrangement of the limestone and granite. 

 Parallel to the limestone bed or beds, and following every flexure 

 and contortion which it undergoes with the most perfect regularity, 

 are to be seen narrow lines rising above the general surface, and 

 accompanying the course of the bed through its whole extent. On 

 examining them they are found to consist of a harder substance 

 which has resisted the action of the water, while the softer and in- 

 termediate parts, being of limestone, have been dissolved and washed 

 away.:}: The fracture of the rock shows that these are the edges of 

 laminse formed of a reddish siliceous substance precisely similar to 

 that which constitutes the reticulations, and which from the contrast 

 of its colour to that of the blue limestone with which it alternates, 

 is always easily distinguished. 



Having blown up a considerable portion of this rock, I am enabled 

 to say that it is of a laminated texture throughout, being a bed 

 of which the alternate layers are limestone and that siliceous red 

 rock which I consider as a modification of granite. A perfect notion 

 of such a limestone may be formed by recollecting the appearances 



* Vide Plate! ^. % Vide Plates 15, 16, 17. 



2l2 



