BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 20, pp. 153-170 April 3, 1909 



FIEST CALCAREOUS FOSSILS AND THE EVOLUTION OF 

 THE LIMESTONES 1 



BY REGINALD A. DALY 



(Read by title before the Society December 29, 1908) 



CONTENTS 



rage 



Introduction 153 



The terrane and the river solute 155 



Effects of the post-Huronian revolution 150 



Analyses of the Ottawa river 157 



Comparison of the Ottawa and other rivers 160 



Chemical contrast of pre-Camhrian and later river systems 161 



Variations in the calcium supply during and after the pre-Cainbrian 162 



The first calcareous fossils 162 



Origin of the pre-Camhrian and early Paleozoic limestones and dolomites. 163 

 Average ratio of calcium to magnesium in the limestones of the different 



periods 163 



Summary on the origin of the pre-Devonian limestones 167 



Testimony of the grain of the pre-Ordovician limestones 167 



General conclusion 168 



Introduction 



It may be assumed that the average water of the ocean has not been of 

 the same composition in any two of the geological periods. The ocean 

 has had a chemical evolution. Though the amount of water may have 

 remained tolerably constant from the pre-Cambrian time to the present, 

 it seems certain that the amount and character of the mineral matter 

 dissolved in the ocean must always have been changing. The inflow of 

 river-borne salts has varied in rate according to the area of the lands and 

 according to the kinds of rocks exposed to subaerial erosion during the 

 different periods. On the other hand, there are reasons for believing 

 that the precipitation of salts from the sea-water (including biochemical 

 precipitation) has occurred at variable rates. The composition of the 

 existing average sea-water may conceivably be dependent on four other 

 factors: a, the primitive condition of the ocean before the regime of the 

 rivers was established; b, the direct solution of submarine rock by sea- 

 water; c, the emission of acids and soluble salts at volcanic vents; and, 



1 Manuscript received by the Secretary of the Society January 8, 1909. 



XII— Bull. Geol. Soc. Am., Vol. 20, 1908 (153) 



