508 THE DEPTHS OF 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- 
boniec acid was conformable to the law of variation with depth 
before referred to :— 
Bottom, 862 fms. 800 fms. 750 fms. 
Oxypen en. s 22 17°79 18°76 
Nitrogen. . . . . 34°50 48°46 49°32 
Carbonicacid . . . 48°28 Sono 31°92 
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 Rockall, 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 
