466 Dr. Mac Culloch on Qjiartz Rock. 



and I can only suggest their suspicious aspect, as a reason for a 

 further examination of them. I am inclined to entertain the same 

 doubts relative to the quartz mountains described by authors in 

 various parts of the world, most of which exhibit the detached 

 and conical forms so often mentioned, and from some of which 

 specimens have come to my hand precisely similar in their minera- 

 logical characters to those which I have described. If such should 

 be the fact, the necessity of finding a place for this rock in the list 

 of formations will be more apparent than before, and it will be the 

 duty of those geologists who lay stress on such distinctions, to 

 ascertain the true rank it ought to bear in their system. 



Schih allien. 



This mountain, already highly interesting from the important 

 geometrical operations performed on it by Dr. Maskelyne, and 

 the subsequent mathematical computations of Dr. Hutton, has 

 again been called into notice by Professor Playfair, in his Lithological 

 Survey, established for the purpose of correcting the results deduced 

 from the labours of those mathematicians. 



As Mr. Playfair's remarks on the geological structure of this moun- 

 tain, although chiefly referring to the particular physical object he 

 had in view, seem to involve some important conclusions respecting 

 the rock described in the two foregoing memoirs, I shall, I trust, be 

 excused for stating the considerations to which they have given rise, 

 and to which I have already alluded, since they may serve to call some 

 further attention to its mineralogical and geological history. 



The mountain itself forms the most elevated part of a ridge which 

 may be considered as rising near Fascally, and extending in a south- 

 westerly direction till it meets that complicated group from which 



