388 THE DEPTHS OF THE SEA. [chap. viii. 



ciently proved that the low temperature is due to 

 a branch of the Labrador current creeping down 

 along* the coast in a direction opposite to that 

 of the Gulf-stream. In the Strait of Florida this 

 cold stream divides — one portion of it passing under 

 the hot Gulf-stream water into the Gulf of Mexico, 

 while the remainder courses round the western end 

 of Cuba. 240 miles from the shore the whole mass 

 of water takes a sudden rise of about 10° C. within 

 25 miles, a rise affecting nearly equally the water at 

 all depths, and thus producing the singular pheno- 

 menon of two masses of water in contact — one 

 passing slowly southwards, and the other more 

 rapidly northwards, at widely different temperatures 

 at the same levels. This abutting of the side of the 

 cold current against that of the Gulf-stream is so 

 abrupt that it has been aptly called by Lieutenant 

 George M. Bache the ' Cold wall.' Passing the cold 

 wall we reach the Gulf-stream, presenting all its 

 special characters of colour and transparency and of 

 temperature. In the section which we have chosen 

 as an example, upwards of three hundred miles in 

 length, the surface temperature is about 20 o- 5 C, 

 but the heat is not uniform across the stream, for 

 Ave find that throughout its entire length, as far 

 south as the Cape Canaveral section, the stream is 

 broken up into longitudinal alternating bands of 

 warmer and cooler water. Off Sandy Hook, beyond 

 the cold wall, the stream rises to a maximum of 

 27 0- 8C, and this warm band extends for about 60 

 miles. The temperature then falls to a minimum of 

 26 0, 5 C, which it retains for about 30 miles, when 

 a second maximum of 27°'4 succeeds, which includes 



