672 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



Summary. 



Premises. — The conclusions emphasized in this chapter are based on the 

 following premises : — 



1. The truth of the evolutionary hypothesis, especially as regards the geo- 

 logically late development of active hunters and scavengers on the general 

 sea floor; 



2. The biologically deduced fact that the evolution of the main animal 

 types, including those secreting hard parts, was accomplished in the ocean ; 



3. The fact that animal types were already highly diversified in Cambrian 

 time; 



4. The experimentally proved fact that representatives of the main animal 

 types can live and thrive in sea water quite deprived of calcium salts; 



5. The postulate that bacterial decomposition of animal remains occurred in 

 Eozoic time and has occurred in all subsequent time; 



6. The experimentally proved fact that bacterial decomposition of animal 

 remains causes the emanation of ammonium carbonate among other products; 



7. The experimentally proved fact that such ammonium carbonate can 

 precipitate from sea water all of its calcium salts in the form of the carbonate 

 and some of the magnesium salts as basic magnesium carbonate. (This pre- 

 cipitation is proved to be actually progressing on the floor of the Black Sea) ; 



8. The experimentally proved fact that the precipitation of magnesium 

 carbonate is facilitated by the absence or low content of calcium salts dissolved 

 in sea water; 



9. The probable fact that, in post-Middle Pluronian (pre-Animikie) time, 

 the land areas and therefore the river systems were greatly increased in size 

 as a result of an orogenfc revolution throughout the earth; much limestone then 

 first exposed to weathering; 



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

 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 secretion 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. 



12. The postulate that the chemical nature of the Ottawa, St. Lawrence, 

 Mississippi, Danube, Rhone, Seine, and other rivers can give a tolerable idea of 

 the necessary and drastic changes in calcium-content which must have 

 characterized the world's river-system as it existed in pre-Cambrian, Paleozoic 

 Mesozoic, and Tertiary times; a comparison of these rivers also showing the 

 relative constancy of the ratio, Ca :Mg, in the average river-waters from the pre- 

 Cambrian to the present time. 



