568 



Dr. W. B. Carpenter on the 



[June 13, 



deep valley, since we passed from 115 to 325 fathoms by merely shifting 

 our position about 7 miles to the northward ; and the heavier water would 

 of course gravitate towards the greater depth, where (Station 7) we found 

 the maximum of density anywhere met with on the Atlantic slope of the 

 " ridge." 



50. Taking these facts in connexion with those to be next stated in 

 regard to the Specific Gravity of the water at different depths within the 

 Strait (i. e. on the Mediterranean slope of the " ridge") and on the " ridge" 

 itself, I cannot but regard it as a fair conclusion that this excess is due to 

 the deep outflow of Mediterranean water over that ridge. It is not a little 

 significant that the effect of this outflow should be so distinctly traceable 

 as far as Station 1, — a fact which seems to me to negative the hypothesis 

 of Captain Spratt, that this dense bottom-water is derived from the remote 

 region of the Atlantic to the south of 30° Lat. : for (1) the excess of eva- 

 poration in that area must be effectually neutralized, in the area between 

 Cape St. Vincent and Mogador, by the vast quantity of fresh water brought 

 down by the Guadiana, the Guadalquiver, and the rivers of Morocco ; whilst 

 (2) all our knowledge of the movement of Oceanic water along the N.W. 

 coast of Africa (§ 63) indicates that it has a southward rather than a 

 northward direction. Further, the Temperature observations made both 

 last year (Report, §§ 75, 76) and this year (§ 62), indicate that any surface- 

 outflow of Mediterranean water is more likely to take place along the 

 European than along the African side. 



51. Proceeding within the Strait, we took up on August 21st our first 

 position off Tarifa, where a sample of water taken from the bottom at 330 

 fathoms gave the high Specific Gravity of 1*0293; clearly showing its 

 Mediterranean character. Samples taken at depths of 200 and 150 

 fathoms gave almost exactly the same Sp. Gr., as did also a second pair of 

 samples taken in nearly the same part of the Strait at 150 fathoms and 125 

 fathoms ; from a comparison of which observations with those taken be- 

 tween Gibraltar and Ceuta (§ 54), it appears that the dense Mediterra- 

 nean water lies about 100 fathoms nearer the surface over a 300 fathoms 

 bottom, than it does where the bottom sinks to more than 500 fathoms. — 

 It was not a little unexpected to find a marked excess in the density of the 

 surface- water in the first set of observations, its Sp. Gr. being as high as 

 1*0275. This seemed attributable to the prevalence of a fresh Easterly 

 wind, producing a westward drift of Mediterranean water that mingled with 

 the surface inflow from the Atlantic ; it must, however, have been local 

 and transient, since at a later part of the day, in nearly the same spot, the 

 Sp. Gr. of the surface-water was found to have returned to its ordinary 

 standard (within the Strait) of 1*0271. — The observations made this day 

 with the Current-drag, although not so continuous or complete as those 

 taken subsequently , made it clear that both the upper and the under-cur- 

 rent are not only greatly influenced in rate, but may be completely 

 reversed in direction, by Tidal agency. One hour after High water, the 



