P. A. Daly — Limeless Ocean of ' Pre- Cambrian Time. 113 



8. The experimentally proved fact that the precipitation of 

 magnesium carbonate is facilitated by the absence or low con- 

 tent of calcium salts dissolved in sea-water ; 



9. The probable fact that, in Eozoic time, the land-areas 

 and therefore the river systems were greatly increased in 

 size as a result of an orogenic revolution throughout the earth ; 

 much limestone then first exposed to weathering ; 



10. The fact that a prolonged period of partial or complete 

 baseleveling followed the mountain-building period, implying 

 a specially great addition of dissolved, river-borne calcium and 

 magnesium salts to the ocean- water. This addition of calcium 

 salts is assumed to have made a fundamental change in the 

 conditions of marine life ; the excess of calcium salts being so 

 great as to permit of the secretions of calcareous shells and 

 skeletons for the first time ; 



11. The fact that the land areas have ever since retained 

 sufficient size and abundance of limestone to furnish the sea 

 with lime salts in excess of the amount of those salts being 

 precipitated by ammonium carbonate and being deposited in 

 the form of organic shells and skeletons on the sea-floor. 



Conclusions. — 1. The lime salts of the ocean, inherited 

 from Azoic times, were precipitated as calcium carbonate com- 

 paratively soon after the introduction of animal life into the sea. 



2. During most of Eozoic time, i. e., pre-Cambrian time in 

 which animal life existed, the ocean was practically limeless ; 

 calcareous secretions by animals were impossible. 



3. Tests and skeletons of pure chitin were possible in Eozoic 

 time, but were not abundantly preserved until some carbonate 

 or phosphate of lime was built into those structures. The 

 calcareo-chitinous tests of Cambrian and Ordoviciah trilobites 

 and shells of b'rachiopods represent a transition stage between 

 the Eozoic aeon of dominantly soft-boclied animals and the 

 post-Cambrian aeon of dominantly lime-secreting animals. The 

 notable fossilization of brachiopocls, trilobites, molluscs, etc., 

 was impossible until near the beginning of Cambrian time. 

 Indeed, the conditions for truly abundant fossilization of cal- 

 careous forms were not established until after the Cambrian 

 period. The striking variety or entire lack of organic remains 

 in the thick Cambrian sediments of British Columbia, Alberta, 

 Idaho and Montana, and in many other parts of the world, 

 may be thus explained. 



4. Eozoic limestones, dolomites, magnesian limestones and 

 calcareous and magnesian deposits generally were chemically 

 deposited through the medium of organic ammonium carbon- 

 ate. This alkali acted on the primeval calcium and magnesium 

 salts of the ocean and on the calcium and magnesium salts 

 introduced to the ocean by pre-Cambrian rivers. A similar 

 origin is suggested for the iron carbonate occurring in Eozoic 



