192 SPARKS FROM A GEOLOGIST'S HAMMER. 



infei'red, therefore, from the four considerations just pre- 

 sented, that the circulation of the ivaters of the sea is not 

 caused directly, as the circulation in the atmosphere is 

 caused. We might, of course, recognize the existence of 

 a necessary tendency to a circulation of the waters, iden- 

 tical with that of the air, and proceeding from the same 

 cause. But the actual circulation is one which demon- 

 strates the existence of some influence which more than 

 countervails such a primary tendency, and establishes 

 identical, instead of conti^ary, movements in the films of 

 water and air which are in contact with each other. On 

 physical principles, however, it does not appear that a 

 circulation would be established in a body of water through 

 the simple application of a warming influence at the upper 

 surface. 



This coincidence between oceanic currents and prevail- 

 ing winds is, indeed, so complete as to suggest a causal 

 relation between the atmospheric and oceanic movements. 

 The suggestion is further sanctioned by all we know of 

 the power of winds to move the surface of the ocean's 

 waters. Who has witnessed a storm at sea without being 

 convinced of this power? Within a few years an easterly 

 wind has so piled up the waters of the Gulf of Mexico 

 alonsj its western border as to inundate and devastate 

 entire cities and villages. We seem quite justified, es- 

 pecially in view of the demonstrated inadequacy of the 

 causes urged by Maury and Carpenter, in pronouncing 

 the sijsteln of prevailing ivinds the phijsical cause of the 

 sijstem of currents. 



Now, it is apparent, in the next place, that the force 

 of the winds the " trades," for example is determined 

 by the difference of temperature between the polar and 



