T^E GEOLOGICAL AGENCY OF THE WINDS. 291 



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 pre- 

 cipitation formerly had, as I suppose they now have, to pass the 

 summits of these mountains, it is easy to perceive wh}^ the winds 

 should not convey as much vapour across them now as they did 

 when the summit of the range v{a,s 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 w-est 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 w^ ith rains ; it is easy to perceive how the whole 

 country to the leeward of such range, and now watered by the 

 vapour which such winds bring, would be converted into a rain- 

 less region. I have used these hypothetical cases to illustrate a 

 position w^hich any philosopher, wdio 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 subsidence of 

 the lake basin itself, or an upheaval of the w^ater-shed drained by 

 it. The cause w^hicli 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. The influence of the South American continent upon the climate 

 of the Dead Sea. — Having therefore, I hope, made clear the 

 meaning of the question proposed, by showing the manner in 

 w^hich wands may become important geological agents, and 

 having explained how the upheaving of a mountain range in one 

 part of the world may, through the wdnds, 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 eleva- 

 tion of the South American continent, and the upheaval of its 

 mountains, to have had any effect upon the water-level of those 



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