748 JOHN JOHNSTON AND E. D. WILLIAMSON 



meter of the earth's surface (sea and land together) is 3 kg. ; for if 

 the proportion of C0 2 in the air at the earth's surface is 3 parts per 

 10,000, the proportion in the whole atmosphere is 2 in 10,000 by- 

 volume, hence 3 in 10,000 by weight, or 3 kg. per square meter. 

 Consequently, since the ocean covers about 71 per cent of the total 

 surface of the globe, the ratio 



total C0 2 in ocean 290X0.71 



total C0 2 in air 



= 69 



In other words, the ocean contains about 70 times 1 as much C0 2 as 

 the air, on the basis of the assumptions specified above. On this 

 basis the total C0 2 now present in the ocean and atmosphere com- 

 bined would form a layer of CaC0 3 only about 17 cm. thick over the 

 whole globe, or about 86 cm. (nearly 3 feet) over one-half the present 

 land area; likewise if the amount of C0 2 in the atmosphere were 100 

 times as much as at present, the corresponding values would be 

 slightly more than 6 times as large, namely, no cm. over the globe, 

 or 550 cm. (18 feet) over one-half the present land area. The 

 possible deductions, however, must remain uncertain until series 

 of simultaneous accurate determinations of free and total C0 2 , 

 temperature, and salinity in the sea at various depths and in different 

 localities shall have been made. 



The precipitation of CaC0 3 in forms other than calcite. — Besides 

 calcite, which is the stable crystalline form of CaC0 3 under all 

 ordinary conditions, there are two unstable crystalline forms, aragon- 

 ite and /x-CaC0 3 , which may precipitate under certain circum- 

 stances. This whole question is discussed at length in another 

 paper, to which the reader desirous of further information is referred ; 2 

 we shall here merely recapitulate the conclusions relevant to the 

 present discussion. The existence of the ju-form in nature has not 

 been definitely established, possibly by reason of the fact that some 

 of the criteria which have been used to differentiate the several forms 

 of CaC0 3 have not been unexceptionable, possibly on account of its 



1 This estimate is higher than that (27 times) of Krogh (Meddelelser om Gronland, 

 XXVI [1904], 420) or that (55 times) given in Chamberlin and Salisbury's Geology, 

 II, 661, which see, with respect to the whole discussion. 



2 "The Several Forms of Calcium Carbonate," Johnston, Merwin, and Williamson, 

 Am. Jour. Sci. (4), XLI (1916), 473. 



