G. M. Dawson — Rocks of British Columbia 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 notless than 10,000 
feet. It is built up of porphyrites, 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 voleanic breecia 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 voleanic ashes and sand, and in the 
region near the eastern flanks of the Coast Kange no intercalated 
siliceous sandstones, or water-leached clays forming true argillites, 
are found. 
It may seem hazardous even to compare roeks 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 resemblanees may to some extent safely Supplement other 
facts. I am not aware that contemporaneous voleanic products have 
been recognized as forming a part of the Cretaeeous or Jurassic 
formations of California, — which of the intermediate region is the 
raost carefully studied portion, — but in reading Professor Whitney’s 
report, one is inuch 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 eomposition as voleanic materials easily liardened and 
crystallized. The “ red rock ” or “ imperfect Serpentine ” of the 
Cretaeeous of the vicinity of San Francisco certainly resembles 
nothing so much as a partly altered voleanic product. 1 
It is evident that by the folding together and complete metamor- 
phism of such masses of voleanic 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 voleanic products with rocks of this dass 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 Yancouver Island, we 
have, in fact, also a great series of rocks of Palmozoic age, almost 
certainly referable to the Carboniferous period, which while com- 
posed of diorites, felsites, schistose and gneissic rocks which Mr. 
1 It should bo mentioned that Prof. J. J. Stepkenson, in reporting on a portion of 
Colorado, speaks of “large fragments of voleanic rocks and voleanic ash in the lower 
portion of the Cretaeeous everywhere.” U.S. Geol. Surv. West of the lOOtli Merid., 
1875, vol. iii. p. 500. 
