Page:Physical Geography of the Sea and its Meteorology.djvu/319

Rh trade-winds of South Africa and America—that these countries, over which theory makes these winds to blow, include all the great deserts of Asia, and the districts of least precipitation in Europe. A line from the Galapagos Islands through Florence in Italy, another from the mouth of the Amazon through Aleppo in Holy Land (Plate VII.), would, after passing the tropic of Cancer, mark upon the surface of the earth the route of these winds; this is that "lee country" (§ 298) which, if such be the system of atmospherical circulation, ought to be scantily supplied with rains. Now the hyetographic map of Europe, in Johnston's beautiful Physical Atlas, places the region of least precipitation between these two lines (Plate VII.).

542. Relays for supplying them with vapour by the way.—It would seem that Nature, as if to reclaim this "lee" land from the desert, had stationed by the wayside of these winds a succession of inland seas to serve them as relays for supplying them with moisture. There is the Mediterranean, with its arms, the Caspian Sea and the Sea of Aral, all of which are situated exactly in this direction, as though these sheets of water were designed, in the grand system of aqueous arrangements, to supply with fresh vapour winds that had already left rain enough behind them to make an Amazon and an Orinoco of. Now that there has been such an elevation of land out of the water, we infer from the fact that the Andes were once covered by the sea, for their tops are now crowned with the remains of marine animals. When they and their continent were submerged—admitting that Europe in general outline was then as it now is—it cannot be supposed, if the circulation of vapour were then such as it is supposed now to be, that the climates of that part of the Old World which is under the lee of those mountains were then as scantily supplied with moisture as they now are. When the sea covered South America, nearly all the vapour which is now precipitated upon the Amazonian water-shed was conveyed thence by the winds, and distributed, it may be supposed, among the countries situated along the route (Plate VII.) ascribed to them.

543. Adjustments in this hygrometry of Caspians.—If ever the Caspian Sea exposed a larger surface for evaporation than it now does—and no doubt it did; if 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 conditions there. And admitting the