Dr. Mac Culloch on Quartz Rock, 463 



and of structure which I have detailed, I think that I am justified 

 in considering this rock, like that of Jura, to be a recomposed, and 

 not a purely chemical deposit, being with it equally ill entitled to 

 the name of granular quartz. Its characters would seem to prove 

 that it has originally been a stratified sandstone, which by some of 

 the revolutions of this globe has been both chemically and mecha- 

 nically altered, consolidated in some places to the apparent loss of 

 its original texture, and so changed in its position as to show but 

 faint indications of its former regularity. 



It now remains to enquire into the connexion of this rock with 

 those which accompany it, a part of the subject, and a very im- 

 portant one, on which I must regret that I have so little precise 

 information to offer. On the sea shore at Kylescuagh, and on the 

 shores of Loch Lowie, a very indurated and compact gneiss appears 

 to lie immediately below the quartz rock, but I could not discover 

 their connexion. In the very centre of the district I found horn- 

 blende slate, gneiss, mica slate, and syenitic granite, together with 

 numerous veins and detached masses of compact epidote» Here 

 also, unfortunately, I could not trace their connexion. Such is 

 the meagre account I have to render of what it would be of prime 

 importance to ascertain, whether these rocks are every where 

 inferior in position to quartz rock, or whether the older schistose 

 rocks do not here, as in other places, alternate with it. Circum- 

 stantial evidence renders the latter probable. In the description of 

 Jura I have remarked that mica slate does, according to Professor 

 Jameson, He above the quartz rock, and Williams considers the rock 

 I have described, which he also calls granular quartz, to be, like 

 granite, the rock on which micaceous schist usually rests. Professor 

 Play fair also in his Illustrations^ (P. 166,) speaks of a " granitic sand- 

 stone In vertical beds," and mentions its alternation with " micaceous 



