REPORT OF THE CHIEF ASTRONOMER 671 



SESSIONAL PAPER No. 25a 



are of similar size.* When solutions of calcium chloride and alkaline (sodium) 

 carbonate react at ordinary temperatures, crystals of calcium carbonate are 

 slowly formed, which reach the same dimensions.! The granules constituting 

 the 'eggs' of the Belt-Cambrian oolites likewise average 0-01 mm. to 0-02 mm. 

 in diameter; the eggs are clearly chemical, inorganic growths. 



In the few places where the Belt-Cambrian carbonate rocks at the Forty- 

 ninth Parallel were observed to have been dynamically metamorphosed, the grain 

 is coarsened.:}: Elsewhere and in general it is reasonable to suppose that we 

 have the original grain more or less perfectly preserved. 



Granting a chemical origin for these carbonate rocks, the genetic problem 

 may be still further narrowed down by excluding the hypothesis of deposition 

 within closed basins or lagoons. The scale of operations was altogether too vast 

 to permit of our crediting the dolomites to the evaporation of sea water. Against 

 that view is, further, the fact that there is no representative of the other 

 inevitably expected evaporation deposits, like rock-salt, associated with the 

 dolomites. 



The hypothesis that the precipitation here occurred through organic decay 

 on the open-sea floor is supported by the discovery of appreciable amounts of 

 carbonaceous matter still resident in the Siyeh and other old limestones in the 

 Boundary section. 



But the choice between the various chemical hypotheses for the Belt- 

 Cambrian and Priest River limestones and dolomites is to be made not simplj* 

 on the basis of facts wholly derived from their study, but rather by the correlation 

 of those facts with the great body of geological principles. The more those 

 principles are developed the more clear is it becoming that strict uniformi- 

 tarianism may err as vitally as the older doctrine of catastrophism. The pre- 

 Silurian carbonate rocks at the Porty-ninth Parallel are entirely different 

 physical and chemical types from the staple modern limestone. It seems, 

 therefore, wrong to confine explanation only to limestone-forming processes now 

 at work. Large-scale geological conditions and processes have had their evolution 

 since Azoic times as surely as plants and animals have been evolved. 



*C. G. Cullis, The Atoll of Funafuti, London, 1904, p. 392; see text, figures and 

 Plate F. 



t H. B. Stocks, Quart. Jour. Geol. Soc, Vol. 58, 1902, p. 54. 



$ In his study of Norwegian marbles, Vogt has found that the rock of finest grain 

 was made up of granules averaging 0.02 to 0-03 mm. in diameter. The grain varies 

 directly with the intensity of the regional metamorpkism suffered by the limestones 

 and dolomites. He divides the marbles into seven classes on this basis, the coarsest 

 marble showing average grains over 5 mm. in diameter. Vogt further states that 

 these dolomitic interbeds are masses which were chemically deposited on the sea floor. 

 From their association with conglomerates and quartzites he notes the implication 

 that these dolomites and limestones are shallow-water deposits. The Norwegian field 

 evidently offers a genetic problem which is similar to that attaching to the Forty-ninth 

 Parallel section. It is therefore, gratifying to the present writer to find his con- 

 clusions so closely parallel to those of Vogt, whose paper was not discovered in the 

 literature until this chapter was ■practically completed. See J. H. L. Vogt, Zeitschrift 

 fur Praktische Geologie, Jan. and Feb., 1898. 



