Subordinate Bock 8. 15 



other rocks of inferior consequence, sucli a« serpentine, 

 quartz, &;c. Granite appears frequently at the boundaries of 

 the central masses in individual beds in the slate series, of 

 whatever nature the latter may be, and its phenomena are 

 generally the same as those of the beds which we have already 

 considered ; but it also occurs at a greater distance (geo- 

 gnostical, not geographical distance reckoned by miles), and, 

 in this case, it is found more rarely in regular beds than in ir- 

 regular masses of all sizes, of which the larger, in reference 

 to the above relations, are to be duly attended to. 



Connected with the granite there are two other mountain- 

 rocks, which, it is true, do not occur everywhere, but w^hen 

 they are met with, are not unfrequently worthy of notice. The 

 first of these is porphyry, the other syenite. We might also 

 include here the greenstones (dolerite and diorite), which, in 

 all their relations, resemble syenite, porphyry, and granite ; but 

 they appear to stand in somewhat nearer connection with other 

 mountain-masses, and hence can be more properly enumerated 

 with them. What are termed trachytes are partly to be con- 

 sidered as porphjTv, partly as granite, and partly as a sort of 

 greenstone, for their determination as a peculiar kind of moun- 

 tain-rock is founded on a purely theoretical assumption, which 

 is proved by no direct observation, and can still less be recog- 

 nised from the nature of the rock. " That kind of porphyry 

 is trachyte which is of Plutonic origin."* 



Porphyry is nothing but a porphyritic granite, whose basis 

 consists of so intimate and fine a compound, that the indivi- 



as Lazol nuts, united together by a cement of very quartzoee clay-slate, 

 is, without doubt, evidently a mechanical rock, at least it is generally regard- 

 ed as such. But it has been observed, that irregular masses of it, like the 

 masses of gi-anite, porphyry, and trap, penetrate the slate-rock (a thin, slaty 

 groywacke-slate), distinctly and decidedly cut through its structure, and, 

 although sharply separated from it, yet closely adhere to it. They do 

 not throw the structure of the slaty rock into the smallest disorder, just like 

 the other rocks mentioned above ; and they present the same phenomena as 

 these. Why should a common origin not be assigned to all these mountain 

 masses 1 As to whether this common origin was Plutonian or Neptunian, 

 or if it can have been one of the two, is another question. 



• Geology and Mineralogy considered with reference to Theology, by the 

 Kers'. "William BucklantU 



