If there was indeed such an ancient ocean, it would have washed the very feet of the precipices on whose summits we are in imagination standing, and below us their recesses would have formed harbors which fancy might fill with commerce, and cities in which we might picture life and movement where all is now dead. It need hardly be said that no telescope has ever revealed their existence (if such ruins, indeed, there are), and it may be added that the opinion of geologists is, as a whole, unfavorable to the presence of water on the moon, even in the past, from the absence of any clear evidence of erosive action; but perhaps we are not yet entitled to speak on these points with certainty, and are not forbidden to believe that water may have existed here in the past by any absolute testimony to the contrary. The views of those who hold the larger portion of the lunar craters to have been volcanic in their formation are far more probable; and perhaps as simple an evidence of the presumption in their favor as we can give is directly to compare such a lunar region as this, the picture of which was made for us from a model, with a similar model made from some terrestrial volcanic region. Here (Fig. 70) is a photograph of such a modelled plan of the country round the Bay of Naples, showing the ancient crater of Vesuvius and its central cone, with other and smaller craters along the sea. Here, of course, we _know_ that the forms originated in volcanic action, and a comparison of them with our moon-drawing is most interesting. To return to our Apennine region (Fig. 69), we must admit, however, when we consider the vast size of these things (Archimedes is fifty miles in diameter), that they are very different in proportion from our terrestrial craters, and that numbers of them present no central cone whatever; so that if some of them seem clearly eruptive, there are others to which we have great difficulties in making these volcanic theories apply. Let us look, for instance, at still another region (Fig. 71). It lies rather above the centre of the full moon, and may be recognized also on the Rutherfurd photograph; and it consists of the group of great ring-plains, three of which form prominent figures in our cut.