168 R. A. DALY THE EVOLUTION OF THE LIMESTONES 



The constituent particles are either idiomorphic and roughly rhombo- 

 hedral, or anhedral and faintly interlocking. The former are everywhere 

 of nearly uniform average diameter, ranging from .01 millimeter to .03 

 millimeter, with an average of about .02 millimeter. The anhedral grains 

 range from .005 millimeter to .03 millimeter, averaging about .015 milli- 

 meter in diameter. 



The same uniform grain was found in the Archean (pre-Belt terrane) 

 dolomites (where unmetamorphosed) at the headwaters of Priest river, 

 Idaho; in the magnesian limestones and dolomites inclosing the pre- 

 'Cambrian chitinous fossil, Beltina danai. in the Clarke (Livingston) 

 range ; and in the Siyeh and Sheppard siliceous limestones of northwestern 

 Montana, which appear to be of Middle Cambrian age. In his account of 

 the Norwegian marbles, Vogt states that the rocks of finest grain are 

 made up of granules averaging .02 millimeter to .03 millimeter in diam- 

 eter, and he distinctly states that the Norwegian dolomites are direct 

 chemical precipitates. 16 



Again, it is important to note that the average diameters of the car- 

 bonate granules are of the same order as the average diameters of calcite 

 and dolomite crystals, which are unquestionably due to chemical precipi- 

 tation from sea-water or saline solutions at ordinary temperatures. Cullis 

 has shown that the calcite granules deposited from sea-water in the cavi- 

 ties of the Funafuti corals have average diameters of from 0.02 to 0.03 

 millimeter ; also that the dolomite crystals, which have gradually replaced 

 the aragonite and calcite of the coral deposits, are of similar size. 17 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. 18 The granules constituting the 

 "eggs'* of the Belt-Cambrian oolites likewise average 0.01 millimeter to 

 0.02 millimeter in diameter; the eggs are clearly chemical, inorganic 

 growths. Finally, it may be noted that a specimen of the Black sea 

 chemically precipitated (teste Andrussow), calcareous mud, when micro- 

 scopically examined by the writer, showed granules of similar range of 

 magnitude. 



General Conclusion 



Notwithstanding the many uncertainties and difficulties of the case, it 

 seems justifiable to use the Ottawa river and other analyses in an attempt 

 to evaluate the great chemical difference between the average river water 



18 J. H. L. Vogt : Zeitschrift fur Praktische Geologie, January and February, 1898. 



17 C. G. Cullis : The atoll of Funafuti, London. 1904, p. 392 ; see text figures and 

 plate F. 



18 H. B. Stocks : Quarterly Journal of the Geological Society, vol. 58, 1902, p. 54. 



