J. D. Dana.on the Volcanoes of the Moon. 339 
face exterior to the cone, is said by Beer and Midler to be of- 
ten but one half or one third the height above the bottom of 
the crater; the outer slopes are generally steep, so that the mar- 
gin appears like a raised rim around the pit. 
Mr. Nasmyth figures one which is filled to its summit, and is 
tipped with a plain 40 miles in diameter ;* looking, he says, as if 
“brim full of molten lava,” having cooled, probably, when thus 
ad 
Fig. 2 
The largest craters are not _ sctiaieia actuated 
Contained in the highest a 
Mountains:. on the contra- === 
ty, they are of less altitude 2==— 
than those of medium size, 
and to a certain extent the 
height varies inversely with 
the diameter. 
= 3 
ZFS 
artificially regular. = Why 
: . SS sb 
are others which consist of ===" a= 
two or. more coalesced cir-  _—Heinsius, seen a little obliquely. 
ignorance alone would presume. 
mption, is to take the first oppor- 
e Mem, of the Roy. Astronom, Soc., XV, 152. 
