Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/72

 Alps. It offers one instance among a thousand others of the little dependence to be placed on the characters of the outline in determining 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 found 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 intimately associated with these, possess also some other natural affinities, 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 investigate 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 distinguishable 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,