ON THE GEOLOGICAL AGENCY OF THE WINDS. 189 



ing southwest winds of the northern hemisphere, should pass over 

 a region of less precipitation generally than they would do if, 

 while performing the office of southeast trades, they had blown 

 over water instead of land. The southeast trade-winds, with their 

 load of vapor, whether great or small, take, after ascending in the 

 equatorial calms, a northeasterly direction ; they continue to flow 

 in the upper regions of the air in that direction until they cross 

 the tropic of Cancer. The places of least rain, then, between this 

 tropic and the pole, should be precisely those places which depend 

 for their rains upon the vapor which the winds that blow over 

 southeast trade-wind Africa and America convey. 



388. Now% if we could trace the path of the winds through the 

 extra-tropical regions of the northern hemisphere, we should be 

 able to identify the track of these Andean winds by the foot-prints 

 of the clouds ; for the path of the winds which depend for their 

 moisture upon such sources of supply as the dry land of Central 

 South America and Africa can not lie through a country that is 

 watered well. 



389. It is a remarkable coincidence, at least, that the countries 

 in the extra-tropical regions of the north that are situated to the 

 northeast of the southeast trade-winds of South Africa and Amer- 

 ica — that these countries, over which theory makes these winds 

 to blow, include all the great deserts of Asia, and the districts of 

 least precipitation in Europe. A line from the Galapagos Islands 

 through Florence in Italy, another from the mouth of the Amazon 

 through Aleppo in Holy Land (Plate VII.), would, after passing 

 the tropic of Cancer, mark upon the surface of the earth the route 

 of these winds ; this is that " lee country" (§ 137) which, if such be 

 the system of atmospherical circulation, ought to be scantily sup- 

 plied with rains. Now the hyetographic map of Europe, in John- 

 ston's beautiful Physical Atlas, places the region of least precipita- 

 tion between these two lines (Plate YIL). 



390. It would seem that Nature, as if to reclaim this " lee" land 

 from the desert, had stationed by the way-side of these winds a 

 succession of inland seas, to serve them as relays for supplying with 

 moisture this thirsty air. There is the Mediterranean Sea, the 

 Caspian Sea, and the Sea of Aral, all of Avhich are situated ex- 

 actly in this direction, as though these sheets of water were de- 

 signed, in the grand system of aqueous arrangements, to supply 



