470 



THE ICE AGE IN NORTH AMERICA. 



With great cogency of reasoning, Mr. Croll shows that 

 the trade-winds are the predominant cause of the present 

 course of the Gulf Stream. After attempting to show the 

 failure of all other theories to account for ocean-currents, and 

 for the direction of the Gulf Stream in particular, Mr. Croll 

 calls attention to the general correspondence between the 

 direction of the winds and that of the great currents of the 

 ocean, and shows how powerful this agency must be in giv- 

 ing motion to the surface of the water, and by constancy of 

 action, finally, to the lower strata of water. Now, from 

 some cause or other, at the present time the southeast trade- 

 winds are considerably stronger than the northeast. As a 

 result, the southeast trades sometimes extend as far as latitude 

 10° or 15° north of the equator ; while the northeast trades 

 rarely extend even as far south as the equator.* The geo- 



Fig. 126. — Map showing course of currents in the Atlantic Ocean, b and b' are currents 

 set in motion by opposite trade winds ; meeting they produce the equatorial current 

 which divides into c. and & continuing on as a and a' and e. 



* CrolPs " Climate and Time," p. 10. 



