61 Dr. Mac Culloch's Sketch of the 



Alps. It offers one instance among a thousand others of the little 

 dependence to be placed on the characters of the outline in deter- 

 mining the nature of mountains, and shows how easily geologists, 

 who have assumed the certainty of such a criterion and used it in 

 their investigations, have been led to deceive themselves, and have 

 contributed to the deception of their readers. But I must proceed 

 to particulars. 



Many varieties of rock are foimd in these mountains, of which 

 some appertain to the trap family more strictly speaking, and others 

 to the clinkstones, a set of rocks which, although they are inti- 

 mately associated with these, possess also some other natural affi- 

 nities, which may render it more convenient to consider them as 

 members of another division. The phenomena to be observed in 

 Sky are however insufficient to illustrate the views on which I am 

 inclined to allot a place for these rocks in the system, for which 

 reason I shall reserve these remarks till another occasion, when 

 more numerous and more explicit facts will enable me to make 

 the evidence proceed hand in hand with the theoretic arrangements 

 to be established on them. I shall therefore content myself with 

 describing the several rocks in a general way, since an attempt to in- 

 vestigate their connections more accurately, would involve too large 

 and unjustifiable a portion of conjecture. 



Greenstone appears to be the most prevalent of the rocks which 

 form this group, and it varies very much in its character in different 

 places. It is often of the most ordinary aspect, consisting of the 

 usual admixtures of hornblende and felspar, and not at all distin- 

 guishable from those which appertain to the stratified parts of the 

 island. This modification passes as usual into one in which the 

 constituent parts, from their minuteness and intimacy of mixture, 



