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 into the slightly heated substratum. Now, as basalt begins to soften at about 1400°F. and the surface of Mars has cooled to at least the freezing-point—perhaps very much below it—the contraction would be so great that if the fissures produced were 500 miles apart they might be three miles wide at the surface, and, if only 100 miles apart, then about two-thirds of a mile wide. But as the production of the fissures might have occupied perhaps millions of years, a considerable amount of atmospheric denudation would result, however slowly it acted. Expansion and contraction would wear away the edges and sides of the fissures, fill up many of them with the debris, and widen them at the surfaces to perhaps double their original size.

Suggested Explanation of the 'Oases.'

The numerous round dots seen upon the 'canals,' and especially at points from which several canals