REPORT OF THE CHIEF ASTRONOMER 673 



SESSIONAL PAPER No. 25a 



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

 were precipitated as calcium carbonate comparatively soon after the introduc- 

 tion 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 so nearly limeless that 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 Ordovician 

 trilobites and shells of brachiopods represent a transition stage between the 

 Eozoic aeon of dominantly soft-bodied animals and the post-Cambrian seon of 

 dominantly lime-secreting animals. The notable fossilization of brachiopods, 

 trilobites, molluscs, etc., was impossible until near the beginning of Cambrian 

 time. Indeed, the conditions for truly abundant fossilization of calcareous forms 

 were not established until after the Cambrian period. The striking rarity or 

 entire lack of organic remains in 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 carbonate. This alkali acted on the primeval calcium and 

 magnesium salts (of the ocean and on the calcium and magnesium salts) intro- 

 duced to the ocean by pre-Cambrian rivers. A similar origin is suggested for 

 the iron carbonate occurring in Eozoic sedimentary beds. It is also suggested 

 that possibly the silica of the cherts and jaspers characteristically associated 

 with these carbonates, were likewise thrown out of solution by ammonium car- 

 bonate of organic origin. The petroleum and natural gas emanations from 

 Eozoic sedimentary rocks receive explanation if the fundamental postuiave oi 

 abundant Eozoic marine life be accepted. 



5. The hypothesis seems to explain the greater development of magnesiaD 

 rocks in the earlier geological formations, especially those belonging to the Eozoic 

 seon. The hypothesis throws light on the formation of dolomitic rocks of all 

 ages. 



6. The ratio of calcium to magnesium is nearly constant in the average 

 limestone of the pre-Cambrian, Cambrian, Ordovician, and Silurian terranes. The 

 ratio increases abruptly in the Devonian limestones, possibly because of the rapid 

 development of the fishes, which then began the more thorough scavenging of the 

 sea floor. 



7. The colonization of the sea floor, at least to the depths where calcium 

 carbonate is not redissolved by pressure, was probably fairly complete in the 

 Cretaceous period. 



8. Magnesium salts first began to be accumulated in the ocean water 

 probably during the early Devonian period. 



9. It is suggested from the facts noted in this chapter that the magnesium 

 now contained in the sea in amount greater than a mere trace began to accumu- 



