illustrating the Distribution of Marine Animals. 213 



and South America, it follows along the western coasts to- 

 wards the equator. The same current, being divided by the 

 southern cape of America, flows also with less volume up 

 the eastern coast, either inside of the warmer tropical current, 

 or else on both sides of it. In the Northern Seas the sys- 

 tem of polar currents is mainly the same, though less regu- 

 lar ; their influence is felt on both eastern and western coasts, 

 but more strongly on the eastern. In the Atlantic the latter 

 reduces the temperature of the waters three or four degrees 

 along the north coast of South America, as far nearly as 

 Cape St Roque. 



The cold currents are most apparent along the coasts of 

 continents and about islands, because they are here brought 

 to the surface, the submarine slopes lifting them upward as 

 they flow on. The limits of their influence towards the 

 equator depends often on the bend of the coast ; for a promi- 

 nent cape or a bend in the outline will change the exposure 

 of a coast from that favourable to the polar current to that 

 favourable to the tropical, or the reverse. Thus it is at 

 Cape Hatteras, on the coast of the United States ; Cape 

 Verde, on Western Africa ; Cape Blanco, on Western South 

 America, &c. 



These are important principles modifying the courses of 

 the oceanic isothermal lines. We may now proceed to the 

 application of them which the best authors afford us, and to 

 some conclusions flowing from the facts. 



In the Atlantic, the warm tropical current flowing west- 

 ward is trended somewhat northward by the northern coast 

 of South America, and still more so by the West India 

 Islands, and thus it gradually curves around to parallelism 

 with the coast of the United States. But south of New- 

 foundland, either wholly from the influence of the colder cur- 

 rent with which it meets, or in part from meeting with sub- 

 marine slopes that serve to deflect it, it passes eastward, 

 and afterwards, where it is again free to expand, it spreads 

 both eastward and north-eastward. The flexures in the iso- 

 crymes of 74 and 68° F., near the United States coast, thus 

 have their origin. For the same reason the line of 56° F. 

 is nearly straight, till it reaches beyond the influence of the 



