500 Concluding Remarks on paet n. 



red orthitic granite now forms, as we have seen, the 

 main part of the Portillo chain : it is injected in dikes 

 not only into the mica- schist and white granites, but 

 into the laminated sandstone, which it has metamor- 

 phosed, and which it has thrown off, together with the 

 conformably overlying coloured beds and stratified 

 conglomerate, at an angle of forty-five degrees. To 

 have thrown off so vast a pile of strata at this angle, 

 is a proof that the main part of the red granite 

 (whether or not portions, as perhaps is probable, 

 previously existed) was injected in a liquified state after 

 the accumulation both of the laminated sandstone and 

 of the conglomerate ; this conglomerate, we know, was 

 accumulated, not only after the deposition of the fos- 

 siliferous strata of the Peuquenes line, but after their 

 elevation and long-continued denudation : and these 

 fossiliferous strata belong to the early part of the 

 Cretaceous system. Late, therefore, in a geological 

 sense, as must be the age of the main part of the red 

 granite, I can conceive nothing more impressive than 

 the eastern view of this great range, as forcing the mind 

 to grapple with the idea of the thousands of thousands 

 of years requisite for the denudation of the strata 

 which originally encased it, — for that the fluidified 

 granite was once encased, its mineralogical composition 

 and structure, and the bold conical shape of the moun- 

 tain-masses, yield sufficient evidence. Of the encasing 

 strata we see the last vestiges in the coloured beds on 

 the crest, in the little caps of mica-schist on some of 

 the loftiest pinnacles, and in the isolated patches of this 

 same rock at corresponding heights on the now bare and 

 steep flanks. 



The lava-streams at the eastern foot of the Portillo 

 are interesting, not so much from the great denudation 

 which they have suffered at a comparatively late period 



