﻿G. M. I)aw&on — Rochs of British Columhia and Chile. 315 



and even in Iquique in Peru, 850 miles north of the southernmost 

 point examined by me in Chile, the Coast escarpment which rises to 

 a height of between 2000 and 3000 feet is thus composed." 



The area over which the Porphyrite formation occurs in British 

 Columbia is very great, but is as yet imperfectly defined. I have 

 roughly estimated its thickness in one locality at not less than 10,000 

 feet. It is built up of porjahyrites, tending occasionally towards 

 quartz porphyries, felsites, and fine-grained dolerites, diabases, and 

 probably also diorites, with other rocks transitional between these 

 and the first named, and great masses of volcanic breccia or agglom- 

 erate. Many of these rocks are of sedimentary origin, as shown by 

 their holding fossils, and by their bedding, but the material has 

 been supplied ready made as volcanic ashes and sand, and in the 

 region near the eastern flanks of the Coast Eange no intercalated 

 siliceous sandstones, or water-leached clays forming true argillites, 

 are found. 



It may seem hazardous even to compare rocks so widely separated 

 in space, but it is very generally found that in directions parallel to 

 the main axis of disturbance on the West Coast, the formations are 

 remarkably constant in character, and it is just in such cases that 

 lithological resemblances may to some extent safely supplement other 

 facts. I am not aware that contemporaneous volcanic products have 

 been recognized as forming a part of the Cretaceous or Jurassic 

 formations of California, — which of the intermediate region is the 

 most carefully studied portion, — but in reading Professor Whitney's 

 report, one is much tempted to believe that a portion of the very 

 puzzling appearance of metamorphism in certain groups of beds 

 intercalated with others almost unchanged, may really be due to 

 their original composition as volcanic materials easily hardened and 

 crystallized. The " red rock " or " imperfect serpentine " of the 

 Cretaceous of the vicinity of San Francisco certainly resembles 

 nothing so much as a partly altered volcanic product. '^ 



It is evident that by the folding together and complete metamor- 

 phism of such masses of volcanic material as those described in Chile 

 and British Columbia, they would form, without addition or much 

 chemical change, a great series of granites, gneisses, diorites, and 

 crystalline schists, like those characterizing many of the older forma- 

 tions in portions of their extent. Besides the mere chemical identity 

 rendering this change possible, it may, I think, be stated that the 

 equivalency of volcanic products with rocks of this class has actually 

 been demonstrated in the field. I would refer especially in this 

 connexion to the work of Prof. Judd in West Scotland, and to that 

 of Mr. J. Clifton Ward in Cumberland. In Vancouver Island, we 

 have, in fact, also a great series of rocks of Palgeozoic age, almost 

 certainly referable to the Carboniferous period, which while com- 

 posed of diorites, felsites, schistose and gneissic rocks which Mr. 



1 It should be mentioned that Prof. J. J. Stephenson, in reporting on a portion of 

 Colorado, speaks of "large fragments of volcanic rocks and volcanic ash in the lower 

 portion of the Cretaceous everywhere." U.S. Geol. Surv. "West of the 100th Merid., 

 1875, vol. iii. p. 600. 



