SKY. GEOLOGY. OVERLYING ROCKS. 365 



clay : an objectionable one, it is true, but capable of 

 serving a temporary purpose. This occurs only among 

 the stratified rocks, and, although generally amygdaloidal, 

 is occasionally simple. 



The compound rock best known to mineralogists as 

 a member of this family, is a mixture of felspar and 

 hornblende, the former presenting two distinct charac- 

 ters, the compact and the crystallized : the term of 

 greenstone is sufficient to distinguish it, and it occurs 

 here both in the mountain masses and among the strati- 

 fied traps. To this compound rock may be added two 

 more, one in which augit, and the other in which hypers- 

 thene, occupies the place of hornblende ; both of which 

 will hereafter be seen to hold conspicuous positions 

 among the rocks of Sky. 



In describing the several members of the unstratified 

 rocks of which I have thus attempted to convey a general 

 idea, I shall commence with the syenite, as there is no motive 

 but that of convenience where there is no natural order. 



The general extent of this rock, and that of the moun- 

 tains composed of it, have already come under review 

 in the account of the face of the country. 



The first consideration, in a geological view, is the 

 connexion which it has with the stratified rocks. On the 

 shore near Broadford it is found for a considerable space 

 distinctly incumbent on the limestone and shale of that 

 series. It is in this place disposed in a flat bedded or 

 laminar manner, and the junction is not attended with 

 any alteration in the texture of the stratified rocks, or 

 any disturbance of their ordinary regularity. It is found 

 in the same manner lying on the same rocks, on the 

 hills between Swishnish and Broadford, often very thin 

 and disposed in patches of very limited extent. These 

 are the only decided instances of its superposition and 

 contact together, which I observed ; and when it is 

 recollected that this tract is nearly the only one of 

 stratified rock which occurs near to it, we must not be 



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