508 THE DEPTHS OE THE SEA. [chap. x. 



carbonic acid and diminution of the oxygen, as the depth 

 increases, the percentage of nitrogen varying but slightly. 



These general results appear to show that the oxygen dimi- 

 nishes and the carbonic acid increases with the depth until the 

 bottom is reached ; but that at the bottom, whatever the depth 

 from the surface, the proportions of carbonic acid and of oxygen 

 do not conform to this law, bottom-water at a comparatively 

 small depth often containing as much carbonic acid and as little 

 oxygen as intermediate water at a greater depth. No instance 

 occurred during the first two cruises in which (where samples 

 of surface and intermediate or bottom-waters were taken at the 

 same place) the quantity of carbonic acid was less and of 

 oxygen greater than at the surface ; the only exception occurred 

 in the third cruise, at a place where, it is believed, currents of 

 water were meeting. 



It was frequently noticed that a large percentage of carbonic 

 acid in bottom-water was accompanied by an abundance of 

 animal life, as shown by the dredge ; and that where the dredge- 

 results were barren, the quantity of carbonic acid was much 

 smaller. The greatest percentage of carbonic acid ever found 

 was accompanied by an abundance of life; while at a short 

 distance (62 fathoms) above the bottom, the proportion of car- 

 bonic acid was conformable to the law of variation with depth 

 before referred to : — 



Bottom, 862 fnis. 



Oxygen ...... 17"22 



Nitrogen 34 - 50 



Carbonic acid . . . 48"28 



100-00 100-00 100-00 



The lowest percentage of carbonic acid (7"93) ever found in 

 bottom-water, occurring at a depth of 362 fathoms, was ac- 

 companied by a " very bad haul." 



In crossing the wide channel from the north-west of Ireland 

 towards Eockall, where the water for some distance is over 

 1,000 fathoms depth, so that the other circumstances varied very 

 little, if at all, the proportion of carbonic acid appeared to vary 

 with the dredge-results ; so that the analyst ventured to predict 



