THE PERMIAN PERIOD. 661 



carbon dioxide in it is very many times greater than the carbon dioxide of the 

 present atmosphere, and probably several times as great as the carbon dioxide 

 of the atmosphere and the ocean combined. The calcium monocarbonate of 

 the present ocean, by estimate, would make a stratum of limestone about i foot 

 thick over the earth's surface, or about 4 feet over one half the present land 

 area. The " loose " carbon dioxide united with this calcium monocarbonate 

 to form bicarbonate, together with all the free carbon dioxide in the ocean, might, 

 by liberal estimate, add 85% to this, if united with calcium to form limestone. The 

 Subcarboniferous limestone mounts up in places to 2500 feet and more in thick- 

 ness, and has a wide distribution on the land, and an unknown distribution beneath 

 the sea. Without doubt we are accustomed to overestimate the mass of such 

 formations, because we dwell upon their maximum, rather than their average 

 or minimum thicknesses, and upon their known distribution in terms of our 

 observational standards, rather than their proportions to the great unknown 

 area of the globe; but yet from the data at hand, it seems inconsistent to assign 

 the Subcarboniferous limestone a mass that is not much greater than the seven 

 and a half feet for an area equal to half the present land, which is all that the 

 present carbon dioxide of air and ocean could produce, if so converted. If we 

 consider what a possible atmosphere and ocean richer in carbon dioxide might 

 do, it seems idle to look to the atmosphere as even a possibly competent reser- 

 voir, consistently with the life that existed; for the carbon dioxide of the present 

 atmosphere, if used up in making limestone,would form a layer of about one thirtieth 

 of an inch thick only, over the globe. To form a layer one foot thick it would 

 have to be increased 360 fold, which would surely imperil active, air-breathing 

 life, unless it were different from similar present life. 



The ocean under certain conditions has much greater competency to hold 

 carbon dioxide, and, what is of prime importance, to hold it in a condition harm- 

 less to animal life. The carbonates of the present ocean, reckoned simply as 

 monocarbonates, hold about 30 times the carbon dioxide of the atmosphere. 

 To this is added a less amount in " loose " combination, to render them bicar- 

 bonates, and an additional quantity held by solution simply. Together, these 

 may be roundly placed at 25 times that of the present atmosphere, giving in 

 all 55 times the present content of the atmosphere. These are merely round 

 figures, roughly approximate. Present data do not permit a close estimate 

 of the " loose " and free carbon dioxide of the ocean. 



The present ocean, however, is not saturated in calcium bicarbonate, for 

 while the specific gravity of the sea ranges from 1.025 to 1.028, calcium car- 

 bonate is not precipitated appreciably until concentration by evaporation reaches 

 1.05, according to the careful investigations of Usiglio. 1 With the existing tem- 

 peratures, it would be possible for the ocean to carry an additional amount of 

 carbon dioxide in the form of bicarbonates, — precisely how much has not been 

 experimentally determined. The higher temperature of the Subcarboniferous 

 ocean would have been adverse; but it is probable that considerably more than 

 55 equivalents of the present atmospheric carbon dioxide might have been held 



1 Enc. Brit. Art. Sea Water, p. 229. 



