316 G. M. Da/vson — Rocks of British Columbia and Chile. 
Selwyn has compared in their lithological character to those of the 
Huronian or Altered Quebec group of Eastern Canada, yet retain 
araple evidence of their origin as volcanic Sediments and igneous 
flows, and hold some beds of crystalline limestone, and of argillite, 
— the latter showing eomparatively Utile sign of alteration. It is not, 
however, intended at this time to enter into detail with regard to 
these rocks, or of the yet more ancient-looking diorites and granites 
of the Cascade Eange, which are very possibly of the same age and 
origin. 
Passing from rocks such as these, however, of which the source is 
yet clearly demonstrable, to some of those of the Eastern border of 
the Continent, one is led to think that sufficient prominence has not 
been given, in endeavouring to account for their origin, to the possible 
inclusion at different periods of great masses of little weathered 
volcanic products ; and that while in Britain the importance of such 
material has been fully recognized, and it has been found to occur 
at many stages in the geological scale, — fonning in Cumberland from 
12,000 to 15,000 feet of “ green slates and porphyries,” in Wales a 
great tliickness of similar hard and more or less crystalline rocks in 
the Lower Silurian alone, — it has scarcely been allowed a foothold 
in Eastern America except in instances so patent that to deny its 
origin would be absurd. In discussing the possibility of the procuc- 
tion of “ metamorphic ” rocks from ordinary aqueous Sediments not 
chemically their equivalents, by pseudomorphism and replacement, 
and the Chemical formation of Sediments by processes not aetive at 
the present day, mucli ingenuity has been employed, while the place 
of volcanos in supplying ready-made the material of crystalline 
rocks has virtually in too many cases been ignored. This action, 
accordiug to strictly nniformitarian principles, must be supposed to 
have been at least as important at former periods as at present, and 
very lately the Challenger soundings have added largely to our idea 
of its influence, Mr. Murray having sliown in connexion with them 
that in point of fact all deposits in the depths of the Pacific not 
organic are volcanic. 
The rocks of the Huronian are, where I have studied them on the 
Lake of the Woods, I have no hesitation in affirming, in great part 
of volcanic origin ; these beds, described originally by Dr. Bigsby 
as “ Greenstone Conglomerates,” being undoubtedly of this character 
and connected with others not so evidently volcanic by trausitional 
material s, the whole associated with some rocks which must have 
approached ordinary argillites in composition and with quartzites. 1 
If correct in this instance, as I believe them to be, similar con- 
elusions will apply to a great portion of the rocks of other localities 
supposed to be of Huronian age, as a perusal of their description in 
the “ Geology of Canada ” will render evident. In the felspathic 
and gabbro-like rocks of the Upper Laurentian, we have a series so 
completely the same in composition with certain abundant modern 
volcanic rocks, that the attempt to account for its composition by 
pseudomorphism, or b} r the theory of Chemical precipitates unlike 
1 Geology and Resources, 49tk Parallel, 1875, p. 52. 
