184 



Messrs. Carpenter and Jeffreys on [Dec. 8, 



perature and Specific Gravity of the bottom-water was conclusive as to its 

 Mediterranean character. Its Density corresponded rather with that of 

 the bottom-water than with that of the intermediate stratum, at the 

 opposite end of the Strait ; but the more rapid Westerly motion of the 

 latter (§ 62) would seem to indicate that the water which here flows 

 over the " ridge " is derived from it, rather than from the deeper layer, and 

 that its diminution in density is due to the dilution it sustains in its 

 course. In either case the denser Mediterranean water discharged by this 

 undercurrent must flow up-hill ; but the incline is so gradual that a very 

 small force, if constantly sustained, would suflice to produce the elevation 

 needed to carry it over the ridge. 



70. Whilst we were prosecuting these inquiries, our attention was at- 

 tracted by the long chains of Aggregate Salpce which were floating close to 

 the Ship near the surface of the very calm sea. We were able to collect 

 four or five different species of these, and to submit them, during life, to 

 Microscopic examination. The reversal of the direction of the Circulation 

 took place in all at more regular intervals than we have usually found to be the 

 case in the Compound Ascidians ; and we were able to distinguish an unmis- 

 takable rudimentary eye, which had not, we believe, been previously noticed. 

 We hope to be able hereafter, by the detailed study of these specimens, 

 to make some additions to the knowledge previously acquired of this very 

 interesting group. — As the nature of the bottom put it out of the question 

 to attempt to dredge on this ridge, our only means of investigating its 

 Zoology lay in the use of the "hempen tangles." A "sweep " taken with 

 these brought up a few Echinoderms and Polyzoa of no special interest ; 

 but with these there was a new species of Amphihelia, allied to A. oculata. 



7 1 . We now took our final leave of the Mediterranean basin with min- 

 gled feelings of disappointment and satisfaction. The Zoological results 

 of our Cruise had been by no means equal to our expectations ; but, on 

 the other hand, we could console ourselves with the belief that our deter- 

 mination of the peculiar Physical conditions of this great Inland Sea, and 

 in particular our elucidation of the mystery of the Gibraltar current, would 

 be fairly regarded as a success ; and we venture to think that this will 

 be admitted by such as may follow us through the discussion of General 

 Results to which we shall presently proceed. 



72. As Capt. Calver considered himself bound not to make any unne- 

 cessary delay in returning homewards, and to take every advantage of the 

 continuance of the fair weather and favourable breeze which we enjoyed 

 during nearly the whole remainder of our voyage, we were reluctantly com- 

 pelled to give up the idea of prosecuting any further researches in the Deep 

 Sea ; and devoted ourselves to the examination of the specimens previously 

 collected, and to the correlation of our Temperature and other results, — spe- 

 cially directing our attention, however, to the Surface-temperature of the 

 embouchure of the Strait, with the view of ascertaining whether a sudden 

 fall would be observable on quitting it, corresponding to the rise which had 



