From St. Thomas to Halifax. 63 



the Labrador current as the latter forces its way southward 

 between the former and the coast of America. 



The two depressions in the isotherms of io° C. and 5 C, 

 noticed in the western half of the section between Teneriffe and 

 Sombrero, may thus be accounted for — at Station 22 by an 

 accumulation of the water of the equatorial current against the 

 inclined base of the Caribbee Islands, and at Stations 18 

 and 17 by the same current forcing its way between the masses 

 of the polar under-current moving in an opposite direction. 

 The undulating form of these isotherms shows that in the 

 western half of the section there are two currents moving in 

 different directions and contending against each other — a form 

 which, at the surface of the ocean, assumes the character of 

 alternating streaks of warm and cold water flowing in opposite 

 directions. This phenomenon is realised on a large scale by 

 the Gulf Stream current, which, in its progress northward, is 

 split up into several branches by the Labrador current, and, as 

 the latter suffers the same fate at the hand of the former, the 

 scene of the contest is covered with alternate streaks of warm 

 and cold water, the one flowing north, the other south. The 

 Agulhas current, off the Cape of Good Hope, and the Kuro- 

 Siwo stream, off the coast of Japan, furnish illustrations of the 

 same phenomenon on a scale not much inferior, and it will occur 

 wherever currents of different origin, and therefore of different 

 temperature, weight, and chemical composition, meet each other. 



For similar reasons, one current may present as solid an 

 obstacle to the progress of another current as if it were a 

 barrier of rock, and compel the latter either to alter its 

 direction or to flow above or below the former — a phenomenon, 

 as will be seen in the course of the following pages, also exhibited 

 on a large scale in the system of oceanic circulation. 



Section from St. Thomas to Halifax (Plate 7, Table II.). 

 — This section extends in a direction nearly due north along 



