430 Dr. Mac Culloch on the Geology of 



arguments drawn from theoretical principles. We have, however 

 a perfect certainty (as far as we have any certainty in geological 

 induction) that it is not stratified, because veins are found arising 

 from it, and entering the mass of incumbent schistus in the well 

 known junction at Loch Ranza. 



I have not thought it necessary to take notice of the probable 

 cause of the prismatic form which occurs so frequently on the 

 summits of the high ridges in this granite, having before spoken 

 of them in my remarks on that of Cornwall and Devonshire. 



I cannot quit this subject without mentioning that many of the 

 masses of granite on the summit of Goatfield, are magnetical, 

 affecting the poles of the needle in sitUy and influencing it also even 

 in detached pieces. This occurrence may probably be more common 

 in granite than we are aware of, but as yet, I believe it has been 

 observed only in the Hartz mountains.* 



Boh arm. 



The sappare (dlsthene) said to have been originally discovered 

 in this place, Is now known to be inherent in many different 

 rocks. Thus, it has been found in granite, in mica slate, and in 

 talc. The specimens of it seen here, occur in a vein of quartz, 

 which traverses a talcy clay slate, a slate accompanied by a 

 singular rock, which I will also describe. It only offers the 

 common aspect of this mineral, which hitherto has exhibited no 

 remarkable varieties, and is of a very decided character. The 

 crystals of disthene occur in the quartz vein, as well as in the clay 

 slate which bounds it, and pass indifferently through both, without 



* I hare since observed it in the mountain Cruachan. 



