1872.] 



' Shearwater ' Scientific Researches. 



577 



(II.) from Tarifa to the eastern entrance to Tangier Bay, a line of about 

 the same length, but about ten miles further west : — 



Pearl Rock 72£° Fahr 



62 

 60 

 59 

 60 

 60 



Point Cires 59^ 



II. 



Tarifa 67° Fahr. 



66 

 64 

 63 

 62 

 62 

 63 

 62 

 62 



Tangier Bay 60 \ 



III. 



Cape Spartel 68° Fahr. 



68 „ 



65 „ 



64 „ 



63 „ 



63 „ 



64 „ 



m „ 



62 „ 



Tangier Bay 60| „ 



Besides these, another Series (III.) was taken along the African coast, 

 between a point a little to the west of Cape Spartel and the western 

 entrance of Tangier Bay. And other observations taken to the S.E. of 

 Europa Point gave temperatures of 72° and 71°*5, which corresponded 

 with those obtained last year near the entrance of the Mediterranean, its 

 proper temperature being here somewhat reduced by the inflow of colder 

 water through the Strait (Report for 1870, § 77). — Hence it appears that 

 whilst the water nearest the Spanish coast in Series I. had the temperature 

 of the Mediterranean, there was a rapid fall in the thermometer as we came 

 into the mid-stream, and a still further reduction occurred towards the 

 African side, — the lowest temperature observed being 13°* 5 beneath the 

 highest, simply in changing our place a few miles to the southward. At 

 Tarifa the influence of the Mediterranean temperature was less marked ; 

 but the temperatures taken near the African side within the embouchure 

 of the Strait were nearly as low as in Series I. 



63. I learn from Dr. Hooker, who has lately visited Morocco, that the 

 prevalence along that coast of a temperature decidedly below that of the 

 opposite coast of Spain, is a fact which has long been known locally ; 

 and that it is indicated at present by the character of the Flora, whilst a 

 still more marked reduction in past times is marked by the Boreal 

 character of the Shells found in the later Tertiary deposits. Looking 

 to the fact that a general southerly set is traceable in the water of this part 

 of the Atlantic, — partly produced, it would appear, by predominant northerly 

 wind-drift, and partly by the indraught requisite to supply the westerly 

 Atlantic drift produced by the Trade Winds (§ 120), — I am disposed to 

 think that the lower temperature of the Gibraltar in-current is due to its 

 original derivation, not from the portion of the Atlantic immediately 

 outside it on the same parallel, but from an area of lower surface-tem- 

 perature to the north-west. But it seems at the same time not impro- 

 bable that just as the water which flows over a mill-dam is drawn, not so 



