CHAP, X.] CONTINUITY OF THE CHALK, 509 
whether the collection would be good or not before the dredge 
came to the surface—drawing his inference from the results of 
his analyses of the gases of the bottom-water. In each case 
his prediction was justified by the result. 
Station 17. Sration 19. SrTation 20. STATION 21. 
1,425 fms. 1,360 fms. 1,443 fms. 1,476 fins. 
Oxycen@- sn 2). Lone 17°92 21°34 16°68 
Nitrogen 5. «48°78 45°88 47°51 43°46 
Carbonic acid. . 35°07 36°20 31°15 39°86 
100°00 100°00 100°00 100°00 
Good haul. Good haul. Bad baul. Good haul. 
In the analyses made of the water in the cold area, and 
generally in the third cruise, there appears, as might be 
expected from the various currents, &c., a greater variation in 
the results than in the other series. In the bottom- and inter- 
mediate waters the nitrogen appears to be rather in excess of 
the average, and the carbonic acid has a large range of varia- 
tion—from 7°58 per cent. at Station 47 (540 fathoms, temp. 
43°8) to 45°79 per cent. at Station 52 (384 fathoms, 30°6 
Fahr.). The average of the surface-waters is much the same as 
in the other parts of the cruise. 
It may be worth notice that in localities where the greatest 
depths did not exceed 150 fathoms, the results of the gas-analysis 
of bottom- and surface-water were frequently so nearly the same, 
whatever the amount of animal life on the bottom, as to lead 
to the supposition that there might be at that limit a sufficient 
circulation, either of the particles of the water itself or of the 
gases dissolved in it, to keep the gaseous constitution alike 
throughout. The coincidence of this depth with the extreme 
depth at which fish are usually found to exist in these seas is 
suggestive. 
Organic matter.—With a view to test the method of analysis 
by permanganate of potash, two or three series of analyses were 
made where fresh and salt water mixed together, as in Killibegs 
Harbour, Donegal Bay, &c.; and the results in all cases justified 
the expectation formed, that the amount of permanganate was 
an index of the comparative purity of the water, both as regards 
the “decomposed” and the “decomposable ” organic matter. 
