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 vapour 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 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 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 subsidence 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. 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 which 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 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 effect upon the water-level of those
