In the same way the 'seas' of the moon present, generally at the edges, rather pronounced depressions.

In one case, as in the other, we observe normal deformations of a shrinking globe shielded from the erosive action of rain, which tends, on the contrary, in all the abundantly watered parts of the earth to make the concave surfaces predominate.

The explanation of this structure, such as is admitted at present by geologists, seems to us equally valid for the moon."[17] [Footnote 17: Comptes Rendus, June 26, July 3, 1899.] It might be urged that there is evidence of former volcanic activity on the moon of such a nature that explosions of steam must have played a part in the phenomena, and if there was steam, of course there was water.
But perhaps the most convincing argument tending to show that the moon once had a supply of water, of which some remnant may yet remain below the surface of the lunar globe, is based upon the probable similarity in composition of the earth and the moon.

This similarity results almost equally whether we regard the moon as having originated in a ring of matter left off from the contracting mass that became the earth, or whether we accept the suggestion of Prof.G.H.Darwin, that the moon is the veritable offspring of the earth, brought into being by the assistance of the tidal influence of the sun.

The latter hypothesis is the more picturesque of the two, and, at present, is probably the more generally favored.