REPORT OF THE CHIEF ASTRONOMER 651 



SESSIONAL PAPER No. 25a 



Since these various waters were working under similar climatic and other 

 solutional conditions, the control of the tei'rane over the amounts of dissolved 

 calcium and magnesium, is manifest. 



After a detailed study of the question Dubois estimates that on an average, 

 ceteris paribus, rivers flowing entirely over silicate rocks carry only one-tenth as 

 much calcium carbonate as rivers flowing entirely over limestone and remarks 

 that even this fraction is almost certainly too large. According to his estimates 

 only one-thirtieth of the calcium carbonate annually entering the sea by the 

 rivers has been newly formed through the decomposition of silicates. The rest is 

 derived from the direct solution of limestone. He has further concluded that in 

 early Archean time the world's river-system probably carried not more than one- 

 eight as much of the carbonate to the ocean as the existing river-system 

 carries. § 



Merely from the quantitative studies of Hanamann and Dubois we may 

 hold, with much confidence, that the annual supply of calcium to the ocean 

 after the revolution was from two to five or more times that characteristic of 

 earlier Huronian and pre-Huronian time. 



The revolution must have had another important effect — in decreasing the 

 sea-bottom area on which the precipitation of calcium carbonate took place. The 

 researches of the 'Challenger' and other oceanographic chemists show that at 

 depths greater than 3,000 fathoms little or no solid calcium carbonate can 

 remain on the sea floor. In fact, the tendency to the complete solution of this 

 salt is strong at all depths greater than 2,500, if not 2,000 fathoms. This means 

 that the permanent removal of calcium carbonate from the present oceanic 

 solution through the decay of animal carcasses at the bottom seems to be possible ' 

 only in about one-half of the existing ocean basin — say 70,000,000 square miles. 

 This area is partly neritic (depths less than 200 fathoms) and partly bathyal 

 (depths between 200 fathoms and 2,000 fathoms). On account of the higher 

 temperatures and lower bottom pressures (pressure increasing the solubility of 

 the carbonate) of the shallower water, we should expect the rate of chemical 

 precipitation of calcium carbonate at the bottom to be concentrated in the neritic 

 (epicontinental) and shallower bathyal regions, a total area of about 35,000,000 

 square miles. 



Let us assume that previous to the Huronian orogenic revolution the 

 whole area of the lands was 20,000,000 square miles, or about 20/55 of the present 

 area. On the view that the ocean has had a nearly constant volume from 

 Huronian times to the present, it follows that the early Huronian sea was largely 

 epicontinental for an area of more than 35,000,000 square miles ; so that the area 

 of rapid chemical precipitation of calcium carbonate was about twice as great 

 as the possible present area. Let us also assume that the Huronian revolu- 



§ E. Dubois. Proc. Section of Sciences, Kon. Akad. van Wetenschappen, Amsterdam, 

 Vol. 3, 1901, pp. 119-126. 



