ON THE GEOLOGICAL AGENCY OF THE WINDS. 227 



mountains as these to be elevated across the track of the winds 

 which supply the lake country with rains ; it is easy to perceive 

 how the whole country to the leeward of such range, and now wa- 

 tered by the vapor which such winds bring, would be converted 

 into a rainless region. 



632. I have used these hypothetical cases to illustrate a posi- 

 tion which any philosopher, who considers the geological agency 

 of the winds, may with propriety consult, when he is told of an 

 inland basin the water-level of which, it is evident, was once high- 

 er than it now is ; and that position is that, though the evidences 

 of a higher water-level be unmistakable and conclusive, it does not 

 follow, therefore, that there has been a subsidence of the lake basin 

 itself, or an upheaval of the water-shed drained by it. 



633. The cause which has produced this change in the water- 

 level, instead of being local and near, may be remote ; it may 

 have its seat in the obstructions to "the wind in his circuits," 

 which have been interposed in some other quarter of the world, 

 which obstructions may prevent the winds from taking up or from 

 bearing off their wonted supplies of moisture for the region whose 

 water-level has been lowered. 



634. Having therefore, I hope, made clear the meaning of the 

 question proposed, by showing the manner in which winds may 

 become important geological agents, and having explained how 

 the upheaving of a mountain range in one part of the world may, 

 through the winds, bear upon the physical geography of the sea, 

 affect climates, and produce geological phenomena in another, I 

 return to the Dead Sea and the great inland basins of Asia, and 

 ask. How far is it possible for the elevation of the South American 

 continent, and the upheaval of its mountains, to have had any ef- 

 fect upon the water-level of those seas ? There are indications 

 (§ 618) that they all once had a higher water-level than they now 

 have, and that formerly the amount of precipitation was greater 

 than it now is ; then what has become of the sources of vapor ? 

 What has diminished its supply? Its supply would be dimin- 

 ished (§ 627) either by the substitution of dry land for water-sur- 

 face in those parts of the ocean which used to supply that vapor ; 

 or the quantity of vapor deposited in the hydrographical basins of 



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