818 J. BARRELL MEASUREMENTS OF GEOLOGIC TIME 



upon iiiaiiy uiicertaiii factors. Walcott, as the result of his discussion, 

 estimates the area of Paleozoic lands supplying calcium to all the seas 

 as 50,000,000 square miles, approximately the present land area of the 

 o-lobe. The area of ocean now accumulating calcareous oozes he takes 

 as 52,500,000 square miles. The area of the Paleozoic epeiric seas in 

 whicli lime accumulated he takes as 13,000,000 square miles, giving a 

 total of 66,000,000 square miles as the total area of deposition at that 

 time.^^ 



"The area over which calcareous depositions was going on during Paleozoic 

 time we have estimated at 66,000,000 square miles, which included the areas 

 of the seas over the continental platform and those of the surrounding oceans. 

 As the conditions appear to have been more favorable for the deposition of 

 lime in the Cordilleran and Appalachian seas, we will assume that it was four 

 times that of the open ocean.^* With a land area of 50,000,000 square miles 

 (ante, page 670) and a rate of chemical denudation of 70 tons per square mile 

 ])er annum, the total calcium contributed to the ocean per year during Paleo- 

 zoic time would be 3,500 million tons, or 3.78 times as much as that estimated 

 for per annum at the present time, which is 925,866,500 tons (ante, page 668). 

 This would have provided 50.7 tons for deposition per annum per square mile 

 in the 65,000,000 square miles of ocean and seas and 202.8 tons for deposition 

 per annum per square mile in the 400,000 square miles of the Cordilleran and 

 600,000 square miles of similar seas. On this basis 81,120,000 tons (36.4 mile- 

 feet) were contributed per annum from the ocean water to the deposit in the 

 Cordilleran sea; adding to this the 42,000,000 tons (18.8 mile-feet) contributed 

 per annum by the denudation of the surrounding area to the Cordilleran sea, 

 we have 128,120,000 tons (55.2 mile-feet) as the amount available for deposit 

 per annum in the Cordilleran sea. At this rate it would have required 16,- 

 300,000 years to have deposited the 2,007,244,800 million tons (900 million mile- 

 feet) of calcium in the Cordilleran sea; adding to this the 1,200,000 years esti- 

 mated for the deposition of the mechanical sediments, we have a total of 17,- 

 500,000 years as the duration of Paleozoic time. 



"In the estimate for the amount of chemical denudation the largest average 

 is taken — 70 tons of calcium per square mile per annum — and the assumption 

 made that all calcium derived from the adjoining drainage was deposited 

 within the Cordilleran sea. Again, the total supply provided per annum to 

 ocean waters of Paleozoic time is taken as 3.78 times greater than the amount 

 annually contributed to ocean waters today; of this, four times as much is 

 assumed to have been taken out per annum per square mile as was taken by 

 the remaining area in which calcium was being deposited. 



ssLoc. cit, pp. 670, 671. 



=* Under the reduction of .~)0 per cent for the interhedded and intermingled mechanical 

 sediments and 25 per cent for other material than calcium deposited from solution, the 

 apparent amount of calcium deposited in the Cordilleran sea was greatly reduced. If 

 this same ratio of reduction is applied to other Paleozoic limestone areas, I douht if 

 over 1,000,000 square miles will he found to contain as large an average amount of cal- 

 cium per square mile as the Cordilleran area. On this account 1,000,000 square miles is 

 the area taken for the greater rate of deposition of calcium during Paleozoic time. — 

 C. D. W. 



