§ 5-iO. THE GEOLOGICAL AGENCY OF THE WINDS. 291 



ter (§ 857) whence tlie rain-winds have been supposed to come. 

 May not the same cause which lessened the precipitation or in- 

 creased the evaporation in the Salt Lake water-shed, have done the 

 same for the water-shed of the great American system of lakes ? 

 If the mountains to the west — the Sierra Nevada, for instance — 

 stand higher now than they formerly did, and if the winds which 

 feed the Salt Lake valley with precipitation formerly had, as I 

 suppose they now have, to pass the summits of these mountains, it 

 is easy to perceive why the winds should not convey as much va- 

 por across them now as they did when the summit of the range was 

 lower and not so cool. The Andes, in the trade-wind region of 

 South America, stand up so high, that the wind, in order to cross 

 them, has to part with all its moisture (§ 297), and consequently 

 there is, on the west side, a rainless region. Now suppose a range 

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

 winds which supply the lake country with rains ; it is easy to per- 

 ceive how the whole country to the leeward of such range, and 

 now watered by the vapor which such winds bring, would be con- 

 verted into a rainless region. I have used these hypothetical 

 cases to illustrate a position 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 higher 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 sub- 

 sidence of the lake basin itself, or an upheaval of the water-shed 

 drained by it. 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. 



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

 The influence of the Questiou proDoscd, bv showiuDf the manner in which 



boutn American con- . i i / »/ o 



^^^^*"pon the cii- wiuds 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 



