XI.] THE SEA AND ITS WORK. 179 



circulation might be established; and it has consequently- 

 been said that every drop of water in the open ocean 

 may, in course of time, be brought up from the greatest 

 depths to the surface. Other meteorological conditions, 

 however, may exert an influence of the same kind, as great 

 as, or even greater than, that produced by difference of 

 temperature. Sir Wyville Thomson regards the influx of 

 cold water into the Pacific and Atlantic Oceans from the 

 south as an indraught due to " the excess of evaporation 

 over precipitation in the northern portion of the land 

 hemisphere, and the excess of precipitation over evaporation 

 in the middle and southern part of the water hemisphere." ^ 



It seems probable that ocean-currents are of no great 

 importance as agents of denudation or of transport. A 

 slow circulation of the entire mass of the ocean, brought 

 about by such comparatively slight differences of density in 

 the water of different parts of tlie ocean, as are here under 

 consideration, might perhaps facilitate the dispersion of the 

 finest sedimentary matter.. Again, where the surface-currents 

 strike upon the shore they must do something in the work 

 of denudation, though as a rule this will be extremely slight; 

 the effect of currents, indeed, is not so much to abrade the 

 land as to carry off the results of its abrasion by other means, 

 and to distribute the finely-suspended matter, far and wide, 

 over the floor of the ocean. 



In addition to the movements of the sea which have 

 been already noted in this chapter — the wind-waves, the 

 surface-currents, and the general circulation — it must not 



Hence it is believed by Sir Wyville Thomson that the greater part of 

 the cold bottom-water in the North Pacific, and a good deal of that in 

 the North Atlantic, is an indraught from Antarctic, and not from Arctic 

 seas. 



^ Proceedings of the Royal Society, vol. xxiv. No. 1 70, p. 470. 



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