GEOLOGIC TIME. 329 



Mr. T. JVrelliird lieade estimates the area of the Paleozoic forniatioiis 

 of l^urope at (i4.-),C()() square miles in the total area of 3,7-!(),r)00 square 

 miles. His estimate of the Paleozoic area is of that which is exposed 

 at the present time and does not include that which is concealed 

 beneath other formations, I think it will be ai minimum estimate to 

 consider that an equal area is covered by the later formations, Avhich, 

 with that exposed, would give in rouiul numbers 1,290,000 square miles, 

 or one-third of the land area of Europe. In North America nearly 

 one-half of the total area was covered by the Paleozoic sea; in South 

 America it was considerably less; and we know too littleof the Asiatic 

 and African continents to place any estimate upon their Paleozoic 

 areas. I think, however, if Ave take one-fourth of the present land 

 area as the territory covered by the Paleozoic seas we shall be con- 

 siderably within the actual amount, even if we add to the surface of the 

 continents the mar<iins of the continental platforms now beneath the 

 sea. Deducting the one-fourth from the total land area, there remain 

 41,250,000 square miles as the land area undergoing denudation during 

 Paleozoic time. Tt may be claimed that large areas in the archipelago 

 region of the I*acitic and in the Arctic ocean may have been land areas 

 at that time. To meet this, 8,750,000 square miles may be added to 

 the 41,250,000 giving a total of 50,000,000 square miles as the land 

 area of Paleozoic time. 



The estimated areas of the various deep-sea deposits of to day con- 

 taining a large percentage of tlie carbonate of lime, are as follows: 

 (xlobigeriua ooze, 40,520,000 square miles, mean percentage of carbonate 

 of lime, 64-53; Pteropod ooze, 400,000 square miles, i)ercentage of car- 

 bonate of lime, 79-26; coral mud and sand, 2,556,000 square miles, 

 mean percentage of carbonate of lime, 80-41. In addition to this. 

 Diatom ooze covers an area of 10,880,000 square miles, with 22-96 per- 

 centage of carbonate of lime; and the mean percentage of carbonate of 

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

 square miles is 19-20. If we consider only those deposits containing 

 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 accunm- 

 lated, was over 13,000,000 square mile-s. It does not appear that there 

 is any good reason to suspect that the area of deposition of t\ie car- 

 bonate 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 stjuare miles as the probable area 

 in which calcium was being deposited in Paleozoic time. 



Conditions favorable for a rapid deposition of the carbonate of lime. — 

 The conditions most favorable for the rapid accumulation or deposition 

 of the carbonate of lime through organic or chemictal agency are warm 

 water and a constant supply of water through circulation by currents. 



