294 THE PHYSICAL GEOGRAPHY OF THE SEA. 



Adjustments in this oratioii tliaii it iiow docs — aiid 110 doubt it did ; if 

 jlfiSs'!™*^ '^ ^ '''' the precipitation in that valley ever exceeded the 

 evaporation from it, as it does in all valleys drained into the open 

 sea, then there must have been a change of hygrometrical condi- 

 tions there. And admitting the vapor-springs for that valley to 

 be situated in the direction supposed, the rising up of a continent 

 from the bottom of the sea, or the upheaval of a range of mount- 

 ains in certain parts of America, Africa, or Spain, across the route 

 of the winds which brought the rain for the Caspian water-shed, 

 might have been sufficient to rob them of the moisture which they 

 were wont to carry away and precipitate upon this great inland 

 basin. See how the Andes have made Atacama a desert, and of 

 "Western Peru a rainless country : these regions have been made 

 rainless simply by the rising up of a mountain range between 

 them and the vapor-springs in the ocean which feed with moisture 

 the winds that blow over those now rainless regions. 



544. That part of Asia, then, which is under the lee of south- 

 coimtriesinthetem- em tradc-wiiid Africa, lies to the north of the tropic 



perate zone of this n r^ t i t i 



hemisphere that are 01 Cauccr, aud bctwecn two Imcs, the one passing 

 in the trade-wind re- through Capc Palmas aud Medina, the other through 



giona of the other .- iT^n'-r*- tt i 



are dry countries. Aden auQ JJelni. iicing extended to the equator, 

 they will include that part of it which is crossed by the conti- 

 nental southeast trade-winds of Africa after they have traversed 

 the greatest extent of land surface (Plate YII.). The range which 

 lies between the two lines which represent the course of the Amer- 

 ican winds with their vapors, and the two lines which represent 

 the course of the African winds with their vapors, is the range 

 which is under the lee of winds that have, for the most part, trav- 

 ersed water surface or the ocean in their circuit as southeast trade- 

 winds. But a bare inspection of Plate YII. will show that the 

 southeast trade-winds which cross the equator between longitude 

 15° and 50° west, and which are supposed to blow over into this 

 hemisphere between these two ranges, have traversed land as well 

 as water ; and the Trade-wind Charf^ shows that it is precisely 

 those winds which, in the summer and fall, are converted into 

 southwest monsoons for supplying the whole extent of Guinea 

 with rains to make rivers of Those winds, therefore, it would 

 seem, leave much of their moisture behind them, and pass along 



* Series of Maury's Wind and Current Charts. 



