ASTRONOMY AND METEOROLOGY. 369 



outside edges elevated above the surrounding plane ; their form is 

 generally regular, and not broken, as those of the preceding class, 

 and the ground around them is elevated in a radiating disposition, as 

 is visible around Tycho, Copernicus, Aristotle, &c. The regularity of 

 their forms suggests that the ejected matter was not disturbed by the 

 motion of waves, and, consequently, that they were atmospherical 

 volcanoes, like those of the Monti Laziali, Albani, and Tusculani, at 

 the south-east of Rome ; the want of breach in the craters seems to 

 indicate that no lava, but only scoriae and loose matters, have been 

 ejected. The disposition of the soil around them suggests the opinion 

 that they are of a comparatively later epoch, and formed after the 

 crust of the satellite was pretty resistant, and was capable of being 

 elevated all round by a great effort. It is singular, indeed, that this 

 radiation of the soil around is found proportional to the magnitude of 

 the central crater. The effect of this soulevement extended some- 

 times to a prodigious distance, comparable to that of the Cordilleras 

 of the Andes on the earth. The greater part of the craters of both 

 the classes now described possesses an insulated rock inside, very sel- 

 dom appearing (at least in commonly good telescopes) perforated. 

 This bears great analogy with what we see in more than one place in 

 the ancient volcanoes of the earth, where the erupting mouth has 

 been stopped by a dome of trachytic matter as by a stump. Monte 

 Yenere, near Rome, is of this formation, and lies in the centre of an 

 immense old crater. 



" The third class of lunar craters is very small, and bears a great 

 likeness with those called by geologists adventitious craters, and seems 

 to be of a very late formation, the last efforts of the expiring volcanic 

 force. They are irregularly scattered through all the moon, but occur 

 more frequently at the borders or inside of the old demolished craters, 

 though not concentric with them, and seem to have been produced 

 after the large ones were completely closed, either by trachytic ejec- 

 tion or by becoming lakes. These small craters have very seldom 

 rocks inside, or a flat bottom ; but their cavity is conical, and does not 

 exceed in dimension our common volcanoes, which are yet active on 

 the earth. From these facts and observations it appears, that volcanic 

 action has gone on in the moon through all the same stages which it 

 has gone and is going on in the earth, and is there probably com- 

 pletely extinguished, on account of the smaller mass of the moon, 

 which has been cooled very rapidly. This rapidity of cooling, joined 

 with the smaller gravity, may account for the great development of 

 volcanism there, and comparatively fewer Plutonian formations. But 

 extensive instances of this kind are not wanting ; the lunar Alps, 

 the Apennines, the Ripheas, &c., may represent this formation, sur- 

 rounding vast basins, and havino- modern volcanoes following the 



cu jj *) 



direction of the higher edges of their chains. Professor Ponzi seems 

 to think it unquestionable that water existed at the surface of the 

 moon ; the fierce glare of the sunshine is not able to melt the ice 

 there, which is probably at the temperature of the planetary spaces ; 

 just as the sun at the surface of the earth is not able to melt our gla- 



