OEIGIN OF CEYSTALLINE EOCKS. 23 



amounts of fresh detrital material, either iu vauished pre-Laureutian coutiueuts, or in vast 

 volcanic centres which have left behind them no traces of their existence. 



This hypothesis further demands a consolidation and recrystallization of the elements 

 of these re-composed rocks, so perfect that the microscope fails to detect the evidence of their 

 detrital origin. The resemblances between the primitive crystalline rocks and what we 

 know to be detrital rocks, compressed, re-cemented, and often exhibiting interstitial mine- 

 rals of secondary origin, is too slight and superficial to deceive the critical student in 

 lithology, and disappears under microscopical examination. The lessons taught by careful 

 lithological and stratigraphical study have already led to the abandonment of the meta- 

 morphic hypothesis by the greater number of geologists ; the more so since, as Bonney has 

 well remarked,** the long-quoted examples of metamorphic secondary and tertiary rocks in 

 Europe have, without exception, been found to be mistaken, and to have been based either 

 on false stratigraphy, on cases of re-composed crystalline rocks, or on a local development 

 of crystalline minerals in the texture of clastic rocks. 



§ 44. The very ingenious metasomatic hypothesis, which would derive the crystalline 

 stratified rocks from the transformation of limestones, is of course a gratuitous one, ba.sed 

 on some observed cases of association of silicates with calcite, and the possible replacement 

 of the one by the others, and deserves mention only as showing the greater difficulties of 

 the previous hypotheses, which could lead to the adoption of that of general metasomatosis. 

 It is possible, however, that its authors never imagined for it the rank of a universal 

 hypothesis ; the creation of continents of pure limestone, and their subsequent transforma- 

 tion into the vast masses of granitoid gneisses just referred to, would make as great 

 demands on our credulity as the metamorphic hypothesis itself. 



As regards the chaotic hyj^othesis of Werner, according to which the whole of 

 the materials of the crystalline rocks were originally dissolved iu a primeval sea, its chemical 

 difficulties are evident to the modern student. That the ocean could have ever held at one 

 time in solution, under any conceivable conditions, the elements of the whole vast series 

 of crystalline rocks, and could have deposited them successively, in that orderly manner 

 which we observe in the earth's crust, was seen to be incredible. This argument, success- 

 fully urged by Playfair and his followers, contributed, with others, to the discredit which, 

 as we have seen, soon fell upon the Wernerian hyi^othesis. 



§ 45. Respecting what we have called the thermochaotic hypothesis, so ingeniously set 

 forth by Daubrée, while his conclusions as to the first precipitation of water on the 

 globe at a very high temperatu.re are not to be questioned, it can, we think, be shown that 

 its direct action, under these conditions, upon the primitive crust could not have resulted 

 in any such succession of deposits as those which make ixp the crystalline schists ; these 

 we are forced to assign to a later period in the history of the globe, for which the phase 

 to which Daubrée has drawn attention was but a prej)aration. 



The mineralogical characters and associations of the ancient crystalline rocks are, it 

 is maintained, incompatible with the elevated temperature suj)posed iu the hyx^othesis of 

 Daubrée. The orderly interstratification with the ancient Laurentian gneisses of beds of 

 limestone, and others of dolomite, not less than the presence in the one and the other of 

 these of concretionary masses and beds of serpentine, after the manner of flint, and the 



** Greological Magazine, November, 1883, p. 507. 



