616 



Dr. W. B. Carpenter on the [June 13, 



128. "We have next to inquire what is the Thermal relation of the Gulf- 

 stream to that of the basin from which it issues ; and what indications are 

 afforded by its Temperature at different Depths as to the Movement of its 

 different strata. — In the first place it is essential to bear in mind that the 

 southward extension of the Polar Current which impinges against the Gulf- 

 stream on the Banks of Newfoundland has been very distinctly traced 

 along the sea-board of the United States, as a distinct band of separation 

 between the coast-line and the Gulf-stream, as far south as the Peninsula 

 of Florida : for although its surface may be warmed by an overflow from 

 the Gulf-stream (as, in the ' Lightning ' channel, the glacial stream from 

 the N.E. is overlain by the warm stream from the S.W.), yet its presence 

 is distinctly indicated by the rapid descent of the thermometer at small 

 depths beneath. Thus off Sandy Hook, where the distance of the Gulf- 

 stream from the coast is about 240 miles (Diagram v. Plate V.), the tem- 

 perature of the surface near the coast is 70° in summer, rises to 75° at 

 about 150 miles distance, and to 83° at about 275 miles, where the section 

 crosses the warmest band or axis of the Gulf-stream : but at a depth of only 

 20 fathoms in this intervening band, the thermometer falls to 60°; at 100 

 fathoms it averages about 47° ; at 200 fathoms it is about 43° ; at 300 

 fathoms from 39° to 42° ; and at 400 fathoms from 37° to 40°. As soon, 

 however, as the "cold wall" has been passed, the thermometer at 20 

 fathoms rises to 77°; at 100 fathoms to 67°; at 200 fathoms to 62°; at 

 300 fathoms to 59° ; and at 400 fathoms to 55° or even 58°.— The breadth 

 of the Polar Stream gradually diminishes, and the rate of its movement 

 decreases ; but that it preserves a steady onward flow is proved by its con- 

 tinuity of temperature, which is distinctly traceable along the whole length 

 of the Floridan Peninsula, from Cape Canaveral, where its breadth is about 

 35 miles, into the Florida Channel itself. For here the Gulf- stream is 

 separated from the American shore-line by a band about 10 miles broad, 

 in which the temperature falls within 100 fathoms to 50°, whilst in the 

 axis of the Stream it averages 75° at that depth ; and very distinct evi- 

 dence of the inward movement of this colder band is afforded by the fact, 

 first pointed out by Prof. Agassiz * and since verified by Capt. E. B. 

 Hunt (of the U.S. Engineers), that the Florida Keys and Reefs are 

 slowly but steadily extending westwards^. During rough weather, the 

 sea about the reefs becomes milky from the stirring-up of the deposit at 

 the bottom ; and this " white water " is invariably drifted to the westward, 

 the matter it carries being slowly deposited both north and south of the 



freer and more direct communication which exists between the deeper parts of the 

 southern portion of the Caribbean Sea and of the outside Atlantic, than that which its 

 northern portion possesses. — Further inquiry into the sub»surface temperature of dif- 

 ferent parts of the Caribbean Sea and the Gulf of Mexico is much to be desired on 

 various grounds. 



* U.S. Coast Survey Eeport, 1851 ; and Appendix 10, p. 145, 1860. 

 f Silliman's American Journal, vol. xxxv. pp. 197-210 & 388-396. 



