GENERAL FEATURES OF THE EARTH. 43 



1. Torrid Zone. — Super-torrid, torrid, and sub-torrid regions. 



2. Temperate Zone. — Warm-temperate, temperate, sub-temperate, cold-tem- 

 perate, and sub-frigid regions. 



3. Frigid Zone. 



They are convenient with reference to the geographical distribution of oceanic 

 animals. 



Since the tropical (the westward) currents are warm, and the 

 extratropical (the eastward) necessarily cold, the elliptical inter- 

 play explained must carry the warm waters away from the equator 

 on the west side of the oceans, and the cold waters towards the 

 equator on the east side. The distribution of temperature thus 

 indicates the currents. In each elliptical circuit, therefore, the 

 line of 68° F. should be an oblique diagonal line to the ellipse ; 

 and thus it is in the North Atlantic, the South Atlantic, the 

 North Pacific, the South Pacific (though less distinctly here, as the 

 ocean is so broad), and the Indian Ocean. The torrid-temperature 

 zones are very narrow to the eastward and broad to the westward. 

 The temperate zones press towards the equator against western 

 Africa and Europe, and western America. On the South American 

 coast this is so marked that a tropical temperature does not 

 touch the whole coast, except near the equator, and does not even 

 reach the Galapagos under the equator off the coast, as shown by 

 the course of the isothermal line of 68°. So in the South Atlantic 

 the colder waters extend north to within six degrees of the equator, 

 where the line of 68° leaves the African coast. The continuation 

 of the Gulf Stream up between Norway and Iceland is shown by 

 the great loops in the lines of 44° and 35°. The effect of the 

 Labrador or polar current in cooling the waters on the coast of 

 America is also well exhibited in the bending southward near the 

 coast of all the lines from 68° to 35°. The polar current is even more 

 strongly marked in the same way 



on the Asiatic coast. The lines E g " __ Q 



from 74° to 35° have long flexures 



southward adjoining the coast, and jr * >^ 



the line of 68° comes down to within / ^*T\' 



15 degrees of the equator. These { ( V.. ^<^Z- U 



waters pass southward mostly as a \^Sr^^^ A 



submarine current, and are felt in \\ )?* , ,' \ 



the East Indies, making a south- i / ^-- , ^ \ 



ward bend in the heat-equator. 



In figure 31 the elliptical line (A'B' AB) represents the course of the current 

 in an ocean south of the equator (E Q). If now the movement in the circuit 

 were equable, an isothermal line, as that of 68°, would extend obliquely across, 



