CHAP. X.] 



CONTINUITY OF THE CHALK. 



507 



Of water at various depths beneath the surface, fifty-nine 

 analyses were made. Those in the first cruise, twenty-six 

 in number, were chiefly from bottom-water at depths from 

 25 to 1,476 fathoms. In the second cruise the twenty-one 

 analyses chiefly belonged to two series, the first of samples 

 taken at intervals of 250 fathoms, from 2,090 to 250 fathoms 

 inclusive; and the second of samples taken at intervals 

 of fifty fathoms from 862 to 400 fathoms inclusive. In the 

 third cruise twelve analyses were made, eight of bottom-water, 

 of which one-half were in the "cold area," and four at inter- 

 mediate depths. 



The general average of the fifty-nine analyses of water taken 

 below the surface gives : 



Percentage. Proportion. 



Oxygen 20'568 100 



Nitrogen 52'240 254 



Carbonic acid . 27'192 132 





100-000 



It will be seen from this that while the quantity of nitrogen 

 is only 1*97 per cent, less than in surface-water, the quantity of 

 oxygen is diminished by 4'48 per cent., and the quantity of 

 carbonic acid increased by 6 '45 per cent. This difference is 

 greater if bottom- waters only are compared with surface-waters. 



The two series of analyses, before referred to, performed 

 during the second cruise upon intermediate waters at successive 

 depths over the same spot, both show a regular increase of the 



