1870.] 



Deep-sea Researches. 



199 



colour being more and more imparted to the general mass of the liquid. 

 The proportion of salt will in time be made uniform throughout the whole 

 column by " diffusion." Now it is obvious that if each column rests (so to 

 speak) on its own base, the degree in which the Salinity of the whole mass 

 is raised by the addition of a more concentrated solution will depend ceteris 

 paribus upon its height ; and thus where the depth of the Mediterranean 

 basin is only between 200 and 400 fathoms, we should expect the Specific 

 Gravity of its water to be more raised by the successive concentration of its 

 surface-films, than where the depth ranges from 1300 to 1700 fathoms. 



95. Since this proves actually to be the case, the further conclusion 

 appears justifiable — that there is an extremely small amount of movement 

 in the abyssal waters of the Mediterranean basin. The uniformity of 

 Temperature throughout the whole of it, and the restriction of seasonal 

 changes in temperature to its upper stratum, will prevent it from being 

 subjected to any thing like the vertical circulation which is produced in 

 the great Oceanic basins by the antagonistic action of Heat and Cold on 

 the Equatorial and Polar areas (§ 125). And from any horizontal dis- 

 placement they would seem altogether excluded by the depth at which 

 they lie ; for the action of winds cannot disturb more than that compa- 

 ratively superficial stratum which is affected by the Gibraltar current. 

 The inflow of lighter surface-water through the Strait, and the outflow of 

 denser water from the comparatively shallow stratum of the neighbourhood, 

 will probably produce no change whatever at depths greater than 500 

 fathoms. And the same may be said of the supply of fresh water brought 

 in either by rain or rivers ; for this will at once go to make up the loss 

 produced by surface-evaporation ; and whilst helping to maintain the 

 purity of the upper stratum inhabited by fishes &c, will do nothing for 

 the waters of the abyssal depths. If these waters were continually subject 

 to horizontal displacement, it might be expected either that the heaviest 

 water would gravitate to the greatest depths, or that the density of the 

 entire contents of the deeper portion of the basin would be equalized; 

 neither of which happens. On the contrary, as just shown, the density 

 varies with the depth in so marked a degree, as to indicate that the water 

 in each part of the basin retains its distinctness from the rest through long 

 periods of time. 



96. Solid Matter in Suspension. — -The water of the Mediterranean is di- 

 stinguished from that of the Atlantic, not only in the larger proportion of 

 Saline matter which it holds in solution, but also in having diffused through 

 its whole mass, in a state of suspension, particles of solid matter in an ex- 

 tremely fine state of division. This statement may seem strange to those 

 who are familiar, either by personal observation, pictorial representation, or 

 verbal description, with the (apparently) clear deep blue of the Mediter- 

 ranean Sea. But the two phenomena will be presently shown not only to 

 be compatible, but to stand to each other in the relation of cause and 

 effect. 



