Reverting now to the moon, we remark that, if the foregoing explanation of the isolated lunar peaks be tenable, it should hold equally for the groups of them which we see in the lunar Apennines, Alps, Caucasus and other ranges of like character. There occur in some places intermediate groups which link the one to the other. Just above the crater Archimedes, on Plate IX., for instance, we see several single peaks and small clumps of them leading by successive multiple-peak examples to what may be called chains of mountains like many that are included in the contiguous Apennine system. And, in view of this connexion between the single peaks and the mountain ranges formed of aggregations of such peaks, it seems to us reasonable to conclude that the latter were formed by the comparatively slow escape of lava through multitudinous openings in a weak part of the moon’s crust, rather than to suppose that the crust itself has been bodily upheaved and retained in its disturbed position. The high peaks that many mountains in such a chain exhibit accord better with the former than the latter explanation; for it is difficult to imagine how such lofty eminences could be erected by an upheaval, and we must remember that the moon has none of the denuding elements which are at work upon the earth, weather-wearing its mountain forms into sharpness and steepness.[12] [Illustration: Fig. 40. SMALL VOLCANIC MOUNTAIN AT THE END OF A STREET AT TENERIFFE.] [Illustration: Fig. 41.] And we have ground for believing the mountain-forming process on the moon to have been a comparatively gentle one, in the fact that the mountain systems appear in regions otherwise little disturbed, and where craters, which have all the appearances of violent origin, are few and far between. Evidently the mountain and crater-forming processes, although both due to extrusive action, were in some measure different, and it is reasonable to suppose that the difference was in degree of intensity; so that while a violent ejection of volcanic material would give rise to a crater, a more gradual discharge would pile up a mountain. In this view craters are evidences of _eruptive_, and mountains of comparatively gentle _exudative_ action.