CHAP. X.] CONTINUITY OF THE CHALK. 505 
average of thirty-two observations upon water at a sufficient 
distance from land to be unaffected by local disturbances was 
1:02779, the maximum being 1:0284 and the minimum 1:0270. - 
It was almost always noticed that, during a high wind, the 
specific gravity of surface-water was above the average. 
The average of thirty observations upon the specific gravity 
of intermediate water was 1:0275, the maximum being 1:0281 
and the minimum 1:0272. 
The specific gravity of bottom-waters at depths varying from 
77 to 2,090 fathoms, deduced from an average of forty-three 
observations, was 1:0277, the maximum being 1:0282 and the 
minimum 1°0267. 
It will be noticed that the average specific gravity of bottom- 
water is slightly less than that of surface-water. In several 
instances the specific gravities of surface- and of bottom-waters 
taken at the same place having been compared, that of the 
bottom-water was found to be appreciably less than that of 
the surface-water. Thus— 
At 1,425 fathoms’ depth (Station 17) it was . . 1°0269 
Suriacerathersaneme es) eo eee ae el cO260 
And 
At 664 fathoms’ depth (Station 266) it was . . 1°0272 
Surlacerababhbersamie: os ats es bens ell ee ean een ee SGOZ80 
According, however, to a series of observations made at the 
same spot (Station 42) at intervals of fifty fathoms, from 50 to 
800, the specific gravity increased with the depth from 1:0272 
at 50 fathoms to 1:0277 at 800 fathoms. 
Several series of specific-gravity observations were made near 
the mouths of rivers and streams; showing the gradual mixture 
of fresh and salt water, and the floating of lighter portions above 
the denser sea-water, as well as the reverse effect produced by 
the influence of tidal currents. Thus outside Belfast Lough a 
rapid stream of water of specific gravity 1:0270 was found above 
water which, at a depth of seventy-three fathoms, had a specific 
gravity of 1:0265. 
Gases of Sea-water.—The analyses of the gaseous constituents 
of sea-water may be divided into two groups: (1) Analyses of 
