530 Concluding Remarks on the pakt ii. 



and by its having been thus more easily sucked into 

 fissures than the other constituent minerals of granite. 

 The strata encasing the flanks of these granitic or 

 andesitic masses, and forming a thick cap on one of 

 their summits, appear originally to have been of the 

 same tufaceous nature with the beds already described, 

 but they are now changed into porcellanic, jaspery, and 

 crystalline, rocks, and into others of a white colour with 

 a harsh texture, and having a siliceous aspect, though 

 really of a feldspathic nature and fusible. Both the 

 granitic intrusive masses and the encasing strata are 

 penetrated by innumerable metallic veins, mostly ferru- 

 ginous and auriferous, but some containing copper- 

 pyrites and a few silver : near the veins, the rocks are 

 blackened as if blasted by gunpowder. The strata are 

 only slightly dislocated close round these hills, and 

 hence, perhaps, it may be inferred that the granitic 

 masses form only the projecting points of a broad 

 continuous axis-dome, which has given to the upper 

 parts of this range its anticlinal structure. 



Concluding Remarks on the Uspallata Range. — I 

 will not attempt to estimate the total thickness of the 

 pile of strata forming this range, but it must amount 

 to many thousand feet. The sedimentary and tufaceous 

 beds have throughout a general similarity, though with 

 infinite variations. The submarine lavas in the lower 

 part of the series are mostly feldspathic, whilst in the 

 upper part, on the summit and western flank, they are 

 mostly basaltic. We are thus reminded of the relative 

 position in most recent volcanic districts of the trachy- 

 tic and basaltic lavas, — the latter from their greater 

 weight having sunk to a lower level in the earth's 

 crust, and having consequently been erupted at a later 

 period over the lighter and upper lavas of the trachytic 

 series. 1 Both the basaltic and feldspathic submarine 

 1 See on this subject Chapter VI. 



