AGENCIES IN DEPOSITION OF CALCIUM CARBONATE 745 



warm and hence comparatively shallow and rising in temperature 

 as they proceed. Consequently, if deposits of CaC0 3 are being 

 formed in this way — and there is no direct evidence at hand which 

 contradicts this view — it should be possible to correlate the position 

 and rate of formation of such precipitated deposits with other things 

 by means of series of bathymetrical observations on the manner of 

 flow of the currents, the temperature of the water, and, above all, 

 the concentration of free C0 2 . As regards the latter, it may be said 

 that the methods hitherto in vogue are very faulty indeed, 1 and that 

 systematic, accurate determinations of the free C0 2 (which can be 

 made by proper choice of method) are very much to be desired, not 

 only on account of their bearing on the present question, but because 

 an accurate knowledge of the concentration of free C0 2 is of high 

 importance 2 in connection with many biological problems, both 

 theoretical and practical. 



Nor would the establishment of this presumed correlation 

 between deposits of CaC0 3 and the physico-chemical conditions pre- 

 vailing in the ocean be of importance only in relation to present-day 

 formations belonging to this category; it would also be of use in 

 interpreting past deposits of this character which have persisted and 

 in co-ordinating them with other factors. For the rate of formation 

 of such deposits (including the limiting case of zero rate) depends 

 obviously upon the mode and rate of circulation of the ocean and 

 the amount of calcium carried by the water rising to the surface, 

 secondarily, therefore, upon the amount of calcium carbonate 

 brought down by the rivers to the sea ; all of which depend ultimately 

 upon the physiographic and petrologic character of the land surface, 

 upon the magnitude of the seasonal variations and regional differ- 

 ences, upon the climate over the whole earth, and upon the propor- 

 tion of C0 2 in the atmosphere. It would lead too far to discuss this 

 question in all its bearings; 3 in order to show the importance of the 



1 See Johnston, Jour. Am. Chem. Soc, XXXVIII (1916), 947. 

 ■ 2 The free and combined CO2 and the alkalinity of the solution are not independent 

 variables, a fact often forgotten; and doubtless many effects ascribed to a change in 

 alkalinity are due equally, or primarily, to a change in the CO 3 equilibrium in the 

 solution. 



3 The discussions of Chamberlin {Jour. Geol., VII [1899], 545, 667, 757), Tolman 

 {ibid., p. 585), Krogh {Meddelelser om Gronland, XXVII [1904], 334), and others, 

 require some revision in the light of data available since that time. 



