206 



Messrs. Carpenter and Jeffreys on 



[Dec. 8, 



charged with the ordinary proportion of salt, there must be a progressive 

 increase in the density of the water of the Mediterranean until it reaches 

 the point of saturation. This objection has been met by another hypo- 

 thesis, viz. that although the surface-water of the Mediterranean shows 

 very little excess of density, there may be a great increase in the propor- 

 tion of salt held in solution in the waters of its abyssal depths ; and it has 

 even been surmised that a deposit of salt is taking place on its bottom. 



109. This hypothesis seemed to derive support from the analysis made 

 by Dr. Wollaston in 1828*, of a sample of bottom-water brought up by 

 Admiral Smyth from a depth of 670 fathoms, at a point about 50 miles 

 within the Strait ; which analysis gave the extraordinary percentage of 

 17*3 parts of Salt, with a Sp. Gr. of 1*1288, — the proportion of Salt in 

 ordinary sea-water being about 3*5 per cent., and its usual Sp. Gr. about 

 1*027. But as Dr. Wollaston's analyses of two other samples of Mediter- 

 ranean water, taken respectively from depths of 450 and 400 fathoms, at 

 distances of 680 and 450 miles eastward of the Strait, showed that their 

 density but little exceeded that of ordinary sea-water, it was pretty clear 

 that the first result was anomalous, and that in whatever way it was to be 

 accounted forf, it did not represent the general condition of the deep 

 water of the Mediterranean. (See §§ 43, 44.) 



110. The inquiries detailed in the previous Section of this Report have 

 conclusively shown (1) That there is a general excess of Salinity in the 

 water of the Mediterranean over that of the Atlantic; (2) That this 

 excess does not pass beyond very narrow limits ; (3) That it is least in 

 surface- water the proportion of salt in which is only about 4*7 per cent, 

 above that contained in the surface-water of the Atlantic; (4) That 

 it is greatest in bottom-w&tev the proportion of salt in which may reach 

 about 9 per cent, above that contained in the bottom-water of the Atlantic, 

 this last not being more — and apparently somewhat less — dense than the 

 surface-water of the same ocean. Our inquiries were almost entirely 

 limited to the Western basin, in which bottom-water of the highest density 

 seemed to prevail at the shallower depths (§93). The single sounding 

 which was taken in the Eastern basin, at a depth greater than any else- 

 where reached, gave us a sample of which the excess was 6*7 per cent. 



111. From these results it seems a justifiable inference that the evapora- 

 tion from the water of the Mediterranean basin is in excess of the amount 

 of fresh water returned into it, occasioning an increase of its density ; but 

 that this increase, notwithstanding the constant influx of salt water from 

 the Atlantic, is in some way kept in check, probably through an efflux of 

 the denser water by an undercurrent, as originally suggested by Dr. Smith 

 in 1673. This is the view adopted by Sir John Herschel (Physical Geo- 

 graphy, 1861, p. 28) ; and it has been considered to derive support from 



* Philosophical Transactions, 1829, p. 29. 



t It was suggested by Admiral Smyth (' Mediterranean,' p. 131) that a brine spring 

 might have been struck upon. 



