187:2.] 



' Shearwater ' Scientific Researches. 



583 



with those obtained last year in the Western Basin (Report for 1870, § 94), 

 as to the fact of the difference in Salinity between the surface- and bottom- 

 water being greatest where the depth is moderate ; and the fact of course 

 becomes yet more significant when the general increase of Salinity is so 

 marked. There appears, then, no reason to doubt the explanation offered 

 last year ; viz. that supposing an equal degree of concentration by surface- 

 evaporation to take place in two or more equal areas, the elevation of the 

 Sp. Gr. of the entire column of underlying water will be inversely propor- 

 tional to the height of that column : for the diffusion of equal amounts 

 of concentrated water through columns whose heights are in the proportion 

 of 1, 2, 3, will raise the Sp. Gr. of these columns respectively in the pro- 

 portion of 3, 2, 1 ; the shortest column being most affected, while the 

 longest, in which the same amount of concentrated water is diffused through 

 three times the quantity, has its density but little raised. 



73. Nature of Bottom. — The character of the bottom indicated by the 

 two deep Soundings which we took in the Eastern basin, corresponded 

 with that which was ascertained last year to prevail in the deeper part of 

 the Western, — the samples of the deposit brought up by the Sounding- 

 apparatus showing it to consist entirely of clayey mud composed of par- 

 ticles in a state of extremely minute division, and the water brought up by 

 the water-bottle from the stratum immediately overlying the bottom being 

 rendered turbid by the presence of like finely divided particles in suspen- 

 sion. Mud of a similar character has been almost universally found by 

 Capt. Spratt* and Capt. Nares (both of whom have been engaged in sur- 

 veying the Eastern Basin of the Mediterranean) at depths exceeding 

 250-300 fathoms; sometimes, however, containing minute Foraminiferal 

 shells. A careful examination of the two samples just alluded to gave no 

 trace either of Foraminifera or of any other Organic forms ; and as it is 

 only in comparatively shallow waters that such traces are met with, I am in- 

 clined to believe that wherever they occur they must have been derived 

 from such a littoral bottom as we found along the Tripoli coast, where 

 Foraminifera abounded at depths of from 100 to 150 fathoms. — The 

 material of the muddy deposit on the bottom of the Eastern basin must 

 probably be for the most part derived from the Nile ; and that it should 

 have exactly the same character near the western border of the basin as 

 it has in much closer proximity to the mouths of that river, is a striking 

 indication of the enormous amount of such material which must be brought 

 down by its current, and of the length of time required for the subsidence 

 of the most finely divided particles. 



74. In my last year's Report (§§ 100-103) I laid great stress upon the 

 slow subsidence of the sedimentary particles, and the turbidity of the bottom- 

 water which is thus produced, as possibly accounting for the scantiness of 

 Animal life on the deep-sea bottom of the Mediterranean ; and I threw it 

 out for the consideration of Geologists, whether the same explanation 



* 'Travels and Researches in Crete,' vol. ii. p. 310. 

 VOL. XX. 2 u 



