G. M. Daivson — Rocks of British Columbia and Chile. 317 
those of the present day, seems almost as unnecessary as it would 
be to invoke a similar remote origin for tbe formation of an ordinary 
sandstone. In suggesting volcanic agency as an important factor in 
the liistory of the Lower Laurentian, more hesitation may be feit, 
as the mere area covered by its rocks is so muck greater than we 
would expect to result from any System or linear series of volcanos as 
at present known. It is still a fact that the greater part of the rocks * 
of that formation are just such as would be produced from the com- 
plete metamorphism of volcanic products among which those of the 
acidic dass preponderated. Its limestones and iron ores do not oppose 
the theory, as these, with the quartzites and graphites may have been 
formed during periods of repose ; and it is also apparent that if con- 
siderable areas of recently ejected volcanic matter were from time 
to time exposed to sub-aerial influences, their decay would furnish 
lime and iron readily and in great abundance to the surrounding 
waters, there to be fixed by organic or other agency. 
Judging from lithological characters alone, and without presuming 
to enter into questions of age, it would appear probable, or almost 
certain, that volcanic Sediments or other more or less immediate 
volcanic products have assisted materially in the production of the 
crystalline rocks of the Green and White Mountains, and their 
probable southward continuations ; the rocks of the Metamorphic 
Quebec group, and those of the supposed Huronian of Eastern 
Massachusetts and Maine. The concise description of these last 
given in Dr. Hunt’s “Chemical and Geological Essays ,” 1 migkt be 
applied with scarcely a word of alteration to portions of the Meso- 
zoic volcanic series of British Columbia. 
If we may be allowed tkus to explain the building up of a great 
tkickness of the older rocks by volcanic action, we may economize 
greatly in the call for geological time, which at present seems 
desirable. The crystalline character of any series of rocks may 
reasonably be supposed to depend more closely on their original 
composition than on subsequent alteration, and in volcanic products 
— which may be as finely stratified as any — we have the materials 
of many of the rocks of the older crystalline formations. If, how- 
ever, the action of volcanos in supplying materials for rock-building 
on a large scale be admitted as possihle at any era in geological time 
— and there is surely no reason why it should not be admitted — the 
coi’relation of separated areas of crystalline rocks on lithological 
characters alone, from the difficulty o,f completely eliminating 
volcanic action, and the precise similarity of the volcanic rocks of 
all periods, when they have sustained an equal degree of altei’ation, 
becomes at least extremely kazardous. On the other kand, as already 
stated, these rocks, due to the same period, may be found at a similar 
stage of metamorphism and skowing precisely similar characters for 
great distances in certain lines of volcanic activity and disturbance, 
and may also be aceompanied by parallel belts of contemporaneous 
materials of ordinary aqueous origin. 
1 p. 187, § 5. 
