164 ON THE CHARACTERS AND DISPOSITION 



of the indurated strata. Nothing can be much more 

 gratuitous than this supposition ; while, even if ad- 

 mitted, it would not explain the formation of these 

 veins in granite and trap. There appears little diffi- 

 culty in tracing them to a watery and gradual infil- 

 tration of the two minerals in question ; whatever 

 objections may be urged against the production of 

 extensive veins of quartz, in this manner. The pro- 

 cess may, in fact, be traced to a sufficient extent, to 

 allow us to infer the possibility of all that is here 

 asked. 



The infiltration of quartz and of carbonat of lime 

 through rocks, is proved by the formation of chal- 

 cedonies, quartz crystals, and calcareous spar, in the 

 inflated cavities of trap rocks ; and in these, every 

 stage of the progress can be traced, as I have fully 

 shown in former writings. It is proved in the case 

 of calcareous spar, by the very common formation of 

 ordinary calcareous stalactites. It is proved that 

 quartz crystallizes from water in these very veins ; 

 because that variety of rock crystal which is formed, 

 like nitre, not by the process of gradual increment on 

 one central nucleus, but by a process commencing in 

 various distant parts at once, often contains water. 

 Lastly, I have traced the actual formation of these 

 veins in primary limestone in Glen Tilt ; where the 

 narrower parts of the fissures were filled by a conso- 

 lidated spar, and the sides of the remainder were co- 

 hered by an incipient crystallization ; the vacancy 

 containing a solution of carbonat of lime. The end 

 of the process can, in such a case, be easily predicted ; 

 and there is no difficulty in applying the same expla- 

 nation to every analogous instance. I ought to add, 

 in terminating this subject, that the same vein some- 

 times contains both quartz and calcareous carbonat ; 



