IG Mr J. D. Dana on the Volcanoes of the Moon. 



The largest craters are not contained in the highest moun- 

 tains : on the contrary, they are of less altitude than those 

 of medium size, and to a certain extent the height varies in- 

 versely with the diameter. 



The pits are generally circular, and sometimes almost arti- 

 ficially regular. There are others vi^hich consist of two or 

 more coalesced circular pits. In still others, especially the 

 largest, the enclosing walls are broken into a series of ridges, 

 sometimes with large openings like the break of an erup- 

 tion ; yet even then the irregular forms may generally be 

 referred either to a single circle, to a combination of circles, 

 or to the formation of successive ridges one within another. 

 The bottom of the pits, though generally flat or nearly so, 

 not unfrequently contains small cones, or ridge-like eleva- 

 tions ; we call them small, though some are 5000 feet in 

 height, for they are mere dots in the immense basin. Over 

 the exterior slopes there are many lateral cones of the same 

 small dimensions, and occasionally one as large as Etna may 

 be distinguished, besides others of different sizes to a few 

 hundred feet in breadth. There are also circular craters 

 within the larger pits, which are of various dimensions. 



The pointed cones or peaks, excepting those immediately 

 connected with the pit-craters, are few in number. Accord- 

 ing to Beer and Madler, JJdrfel, the most elevated lunar 

 peak measured, is 24,945 feet in height ; it is situated in the 

 lunar Apennines : Huygens, another peak, is 18,209 feet in 

 altitude. 



The mountain ridges are peculiar in being generally elon- 

 gated elevations, or clusters of such elevations, without val- 

 leys intersecting their declivities, and thus very unlike the 

 chains of our globe. As M. Rozet and others have remarked, 

 there is no water on the moon to wear out valleys. 



Many of the depressions called seas, of which the Mare 

 Serenitatis, and Mare Crisium, are examples, vary in breadth 

 to five or six hundred miles, and, notwithstanding their size, 

 they are identical in character with the great pit-craters, 

 their extent and less depth being their only characteristics. 

 This view is suggested by M. Rozet, and their features 



