670 THE JOURNAL OF GEOLOGY. 



The area of dry land to-day is estimated to be 55,000,000 

 square miles, and of oceans 137,200,000 square miles. 1 



Mr. T. Mellard Reade estimates the area of the Paleozoic 

 formations of Europe at 645,600 square miles in the total area of 

 3,720,500 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 a minimum estimate to consider that an equal area is 

 covered by the later formations, which, with that exposed, would 

 give in round 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 little of the 

 Asiatic and African continents to place any estimate upon their 

 Paleozoic areas. I think, however, if we take one-fourth of the 

 present land area as the territory covered by the Paleozoic seas 

 we shall be considerably within the actual amount, even if we 

 add to the surface of the continents the margins of the continen- 

 tal 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. It 

 may be claimed that large areas in the archipelago region of the 

 Pacific 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 milesas the land 

 area of Paleozoic time. 



The estimated areas of the various deep sea deposits of 

 to-day, containing a large percentage of the carbonate of lime, 

 are as follows : Globigerina ooze, 49,520,000 square miles, mean 

 percentage of carbonate of lime, 64.53 ; Pteropod ooze, 400,000 

 square miles, percentage of carbonate of lime, 79.26 ; Coral mud 

 and sand, 2,556,000 square miles, mean percentage of carbonate 

 of lime, 86.41. In addition to this, Diatom ooze covers an area 

 of 10,880,000 square miles, with 22.96 percentage of carbonate 

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

 'Dr. John Murray: Scottish Geog. Mag., Vol. 4, 1888, p. 40. 



