40 PHYSIOGRAPHIC GEOLOGY. 



In the North Atlantic, the deep tropical current from the east is 

 turned to the northward along the West India islands, and there be- 

 comes the Gulf Stream ; it flows by Florida to the northeast, follow- 

 ing nearly the outline of the oceanic basin; it passes the New- 

 foundland bank, and stretches over toward Europe ; then a part bends 

 southeastward to join the tropical current and complete the ellipse, 

 the centre of which is the Sargasso Sea, abounding in seaweeds 

 and calms. Another large portion continues on northeastward, over 

 the region between Britain and Iceland, to the poles. From the polar 

 region, it returns along by Eastern Greenland, Davis' Straits and other 

 passages, pressing against the North American coast, throwing cold 

 water into the Gulf of St. Lawrence, bringing icebergs to the New- 

 foundland banks, and continuing on southward to the West India 

 islands and South American coast, where it produces slight effects in 

 the temperature of the coast-waters. Cape Cod stands out so far that 

 the influence of the cold current is less strongly felt on the shores 

 south than north ; and Cape Hatteras cuts off still another portion. 



In the South Atlantic, there is the tropical flow from the east ; the 

 bending south toward Rio Janeiro ; the turn across toward Cape of 

 Good Hope ; and the bending again, northward, of the waters now 

 cold. But, owing to the manner in which the channels of the South 

 Atlantic and North Atlantic are united, a large part of the tropical 

 current of the former goes to swell the tropical current and Gulf 

 Stream of the latter. 



In the North Pacific, there is the same system, modified mainly by 

 this, that the connection with the polar regions is only through the nar- 

 row and shallow Behring Straits. There is a current answering to the 

 " Gulf Stream " off Japan, and another corresponding to the " Labra- 

 dor current " along the whole length of the Asiatic coast, perceptible 

 by the temperature if not by the movement. 



In the South Pacific, there are traces of a " Gulf Stream " — that 

 is, of an outward-bound tropical current — off Australia, noticed by 

 Captain Wilkes. The inward extratropical current, chilled by its 

 southern course, is a very important one to Western South America, 

 as it carries cool waters quite to the equator. 



In the Indian Ocean, the system exists, but with a modification de- 

 pending on the fact that the ocean has no extended northern area. 

 The outward tropical current is perceived off southeastern Africa. 



The surface-currents of the ocean are more or less modified by 

 changes in the winds. On this and on other related topics barely 

 glanced at in this brief review, the reader may refer to treatises on 

 Meteorology or Physical Geography. 



(2.) Oceanic temperature. — The movement of the oceanic cur- 



