GEOLOGIC TIME. 67 1 



Blue Mud and other terrigenous deposits that cover 16,050,000 

 square miles is 19.20. If we consider only those deposits con- 

 taining over 64 per cent, of carbonate of lime, we have 

 52,500,000 square miles, over which there is at the present time 

 a deposition of the carbonate of lime being made. We have 

 roughly estimated that in Paleozoic time the area of the Paleozoic 

 sea, in which deposits were being accumulated, was over 13,000,- 

 000 square miles. It does not appear that there is any good 

 reason to suspect that the area of deposition of the carbonate of 

 lime in the open ocean during Paleozoic time was not fully equal 

 to that of the present time. Adding this area of 52,500,000 to the 

 13,750,000, we have over 66,000,000 square miles as the probable 

 area in which calcium was being deposited in Paleozoic time. 



Conditions favorable for a rapid deposition of the carbonate of 

 li?ne. — The condition most favorable for the rapid accumulation 

 or deposition of the carbonate of lime through organic or 

 mechanical agency is warm water and a constant supply of 

 water through circulation by currents ; this is shown by the 

 immense abundance of life where the margin of the continental 

 plateau is touched by the Gulf Stream. Another favorable con- 

 dition is the supply of carbonate of lime by river water directly 

 into the ocean in the vicinity where the deposition of lime is 

 going on either through organic or inorganic agencies. This is 

 well illustrated by the conditions produced by the Gulf Stream. 

 The oceanic currents, passing along the northeastern coast of 

 South America, sweep the waters of the Amazon through the 

 Caribbean sea into the Gulf of Mexico, where they meet the 

 vast volume of water coming from the Mississippi. These are 

 poured out through the narrow straits between Florida and Cuba 

 and carried northward over the sloping margin of the continental 

 plateau. Under such favorable conditions the deposit must be 

 much greater than in areas where there is little circulation and 

 the supply of calcium is limited to the average which is con- 

 tained in sea water. If to the preceding there is added extensive 

 evaporation within a partially enclosed sea, the rate of deposition 

 of matter in solution will be largely increased. 



