82 Mi* J. D. Dafltt on the Volcanoes of the Moon. 



feature is, therefofe, never exemplified on the earth oti tlie 

 same grand scale as in the moon.* 



We may, therefore^ say unhesitatingly, without fearing an 

 impeachment of our sobriety, that the moon's volcanoes arc 

 in fact volcanoes, either extinct or active, although the cra- 

 ters would receive comfortably more than a score of Etnas. 

 AVe also comprehend the important fact, that a cooling globe 

 would become at first a scene of great boiling lakes from tlic 

 hardening of some portions ; — tliat on a farther diminution 

 of heat, these lakes would partially cool, excepting points or 

 areas of greatest heat, and thus a subdivision of them would 

 result ; or else, they would gradually/ contract their overflow- 

 ings, and so, as gradually, contract the size of the vent, obli- 

 terating all evidence of the former size : or again, they would 

 more abruptly contract, and, consequently, form an inner 

 ledge concentric with the outer walls, and perhaps also other 

 concentric ledges still smaller. 



This is well illustrated in the figures, and nothing could 

 better indicate the mode of action which characterizes the 

 moon's craters, for we may trace out the successive diminu- 

 tions. In Heinsius (fig. 3), which is forty-eight miles in its 

 longer diameter, this is beautifully shewn ; there is one low 

 ledge within another nearly concentric, and finally a smaller 

 bircular pit, of twelve miles breadth, — no mean size, though 

 we call it small. An outer concentric ridge is also apparent 

 through part of its circuit, which may have been a still ear- 

 lier outline ; and being lower than the ridge next within, it 

 illustrates the statement, if the hypothesis be true, that the 

 larger craters have lower walls. It is, however, possible 

 that it may have resulted from a subsidence in the area 

 around, as has happened at Kilauea. The same facts are 

 fetill shewn by the mountains Ahulfeda and Timocharis ; and 

 we have already remarked that the crater of the last men- 

 tioned has very nearly the features of the Kilauea pit. Again, 

 they might finally so far diminish their size by the cooling 

 in progress, that there would no longer be free ebullition, and 

 the vapours having to force their way up, would break 



* The elevation theory of Von Buch has been 6upj)ortecl from facts in the 

 moon. We offer nothing here on that subject. 



