I listened with attention, for I knew that my companion was a man of science, as of experience and observation, and subjects of the character of those about which we conversed had always possessed great interest for me. He continued-- "There can be no rain without vapour in the air. There can be no vapour in the air without water on the earth below to produce it. Here there is no great body of water. "Nor can there be. The whole region of the desert is upheaved--an elevated table-land. We are now nearly six thousand feet above sea level. Hence its springs are few; and by hydraulic law must be fed by its own waters, or those of some region still more elevated, which does not exist on the continent. "Could I create vast seas in this region, walled in by the lofty mountains that traverse it--and such seas existed coeval with its formation; could I create those seas without giving them an outlet, not even allowing the smallest rill to drain them, in process of time they would empty themselves into the ocean, and leave everything as it now is, a desert." "But how? by evaporation?" "On the contrary, the absence of evaporation would be the cause of their drainage. I believe it has been so already." "I cannot understand that." "It is simply thus: this region possesses, as we have said, great elevation; consequently a cool atmosphere, and a much less evaporating power than that which draws up the water of the ocean. Now, there would be an interchange of vapour between the ocean and these elevated seas, by means of winds and currents; for it is only by that means that any water can reach this interior plateau. That interchange would result in favour of the inland seas, by reason of their less evaporation, as well as from other causes. We have not time, or I could demonstrate such a result. I beg you will admit it, then, and reason it out at your leisure." "I perceive the truth; I perceive it at once." "What follows, then? These seas would gradually fill up to overflowing. The first little rivulet that trickled forth from their lipping fulness would be the signal of their destruction. It would cut its channel over the ridge of the lofty mountain, tiny at first, but deepening and widening with each successive shower, until, after many years--ages, centuries, cycles perhaps--a great gap such as this," (here Seguin pointed to the canon), "and the dry plain behind it, would alone exist to puzzle the geologist." "And you think that the plains lying among the Andes and the Rocky Mountains are the dry beds of seas?" "I doubt it not; seas formed after the upheaval of the ridges that barred them in, formed by rains from the ocean, at first shallow, then deepening, until they had risen to the level of their mountain barriers; and, as I have described, cut their way back again to the ocean." "But does not one of these seas still exist?"