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 VII.). 
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 which 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 
