"The Great Salt Lake? It does. It lies north-west of us. Not only one, but a system of lakes, springs, and rivers, both salt and fresh; and these have no outlet to the ocean. They are barred in by highlands and mountains, of themselves forming a complete geographical system." "Does not that destroy your theory?" "No. The basin in which this phenomenon exists is on a lower level than most of the desert plateaux. Its evaporating power is equal to the influx of its own rivers, and consequently neutralises their effect; that is to say, in its exchange of vapour with the ocean, it gives as much as it receives. This arises, not so much from its low elevation as from the peculiar dip of the mountains that guide the waters into its bosom. Place it in a colder position, _ceteris paribus_, and in time it would cut the canal for its own drainage. So with the Caspian Sea, the Aral, and the Dead Sea. No, my friend, the existence of the Salt Lake supports my theory. Around its shores lies a fertile country, fertile from the quick returns of its own waters moistening it with rain. It exists only to a limited extent, and cannot influence the whole region of the desert, which lies parched and sterile, on account of its great distance from the ocean." "But does not the vapour rising from the ocean float over the desert?" "It does, as I have said, to some extent, else there would be no rain here. Sometimes by extraordinary causes, such as high winds, it is carried into the heart of the continent in large masses. Then we have storms, and fearful ones too. But, generally, it is only the skirt of a cloud, so to speak, that reaches thus far; and that, combined with the proper evaporation of the region itself, that is, from its own springs and rivers, yields all the rain that falls upon it. Great bodies of vapour, rising from the Pacific and drifting eastward, first impinge upon the coast range, and there deposit their waters; or perhaps they are more highly-heated, and soaring above the tops of these mountains, travel farther. They will be intercepted a hundred miles farther on by the loftier ridges of the Sierra Nevada, and carried back, as it were, captive, to the ocean by the streams of the Sacramento and San Joaquim. It is only the skirt of these clouds, as I have termed it, that, soaring still higher, and escaping the attractive influence of the Nevada, floats on, and falls into the desert region. What then? No sooner has it fallen than it hurries back to the sea by the Gila and Colorado, to rise again and fertilise the slopes of the Nevada; while the fragment of some other cloud drifts its scanty supply over the arid uplands of the interior, to be spent in rain or snow upon the peaks of the Rocky Mountains. Hence the source of the rivers running east and west, and hence the oases, such as the parks that lie among these mountains. Hence the fertile valleys upon the Del Norte, and other streams that