"Others have suggested that the hot sun causes the growth of some kind of vegetation all over the plain, the ripening of which makes the floor darker in tint. As regards this suggestion, it is the fact that upon Mars the old sea-beds are the places where vegetation is most luxuriant at the present time; so, if Plato were at one time an enclosed sea, it might not be impossible that vegetation in some low form might grow and be nourished by the crude gaseous remains of a former atmosphere. A greenish tint has occasionally been noticed by some observers, also several light streaks across the floor, as well as several small craterlets, which have been duly noted on the maps.
"But before we go any further we will have a better means of seeing, for it is rather uncomfortable looking directly down upon the moon. So, John, just lend a hand and we'll fetch one of those large mirrors."
This was done, and the mirror suspended with the upper part projecting forward, so that when adjusted at the proper angle we could sit and look straight into the mirror before us and see the reflection of all that was below. We could still look down at the objects, if we wished to do so, without shifting our position.
"There, John," I remarked, as we completed this arrangement, "I have already arranged mirrors in the proper positions at the windows in the forepart of the vessel, so that in future M'Allister will be able to see what is nearly straight ahead of him. Now you will understand that I had a scientific use for the mirrors I provided, and did not require them merely to admire my beautiful face in as you suggested."
John laughed as I recalled his suggestion, saying, "All right, Professor, I know you generally have a good reason for what you do."
Now, being more comfortably seated, I drew their attention to some small isolated mountains on the area to the south of Plato, pointing out Pico, an isolated mountain over 8000 feet in height, and another with three peaks not very far from it. To the north-east of these, some distance away, are the Teneriffe and Straight Ranges; also isolated groups.
"You will remember," I remarked, "that I said there were several formations which seemed to me to owe their present appearance to the action of water. Now look well at all this district before us—does it not seem to bear out my contention? Those numerous small mountains and isolated groups were not, I think, originally isolated, but connected with the adjoining ranges. If we assume that Plato was once an enclosed sea, or lake, which burst through the mountain walls—possibly owing to their being weakened or broken by volcanic action—there would have been a tremendous outrush of water, which must have carried away a good deal of the softer material of these hills and mountains; whilst, in after years, the continual wash of the waters, combined with aerial denudation, would gradually have worn away all but the hardest parts of these formations.
"Most probably the whole of the surrounding area was also at some time a sea, though volcanic action has since altered its surface conformation, and in places it bears evidence of having been covered with lava. It is not unusual on our world for volcanoes to burst up from under the sea, so even the evidence of volcanic action does not, as some seem to think, negative the possibility of water ever existing here; and it may not be inappropriate to point out that our hydrographers have proved that our ocean-beds are not always smooth, but are often diversified by high hills and deep valleys."
M'Allister here interjected: "Professor, would you kindly tell us something about that fine range of mountains over yonder, just to the right hand?"
"Oh yes," I replied; "I was just about to mention that mountain range, which is called the Alps after those in Switzerland; and that peak on the front portion, just south of the great valley you see, is named Mont Blanc, and is about 12,000 feet in height.