chap. xv. The Chilian Cordillera. 585 



pared with the erupted beds, often of submarine origin, 

 but not metamorphosed^ which compose the numerous 

 islands in the Pacific, Indian, and Atlantic Oceans ; for 

 in these islands metals are entirely absent, and their 

 nature even unknown to the aborigines. 



Summary on the Geological History of the Chilian 

 Cordillera, and of the Southern Parts of South 

 America. 



We have seen that the shores of the Pacific, for a 

 space of 1,200 miles from Tres Montes to Copiapo, and 

 I believe for a very much greater distance, are com- 

 posed, with the exception of the tertiary basins, of meta- 

 morphic schists, plutonic rocks, and more or less altered 

 clay-slate. On the floor of the ocean thus constituted, 

 vast streams of various purplish clay-stone and green- 

 stone porphyries were poured forth, together with great 

 alternating piles of angular and rounded fragments of 

 similar rocks ejected from the submarine craters. From 

 the compactness of the streams and fragments, it is 

 probable that, with the exception of some districts in 

 Northern Chile, the eruptions took place in profoundly 

 deep water. The orifices of eruption appear to have 

 been studded over a breadth, with some outliers, of 

 from 50 to 100 miles : and closely enough together, 

 both north and south, and east and west, for the ejected 

 matter to form a continuous mass, which in Central 

 Chile is more than a mile in thickness. I traced this 

 mould-like mass, for only 450 miles ; but judgiug from 

 what I saw at Iquique, from specimens, and from 

 published accounts, it appears to have a manifold 

 greater length. In the basal parts of the series, and 

 especially towards the flanks of the range, mud, since 

 converted into a feldspathic slaty rock, and sometimes 



