Professor Secchi's Description of Lunar Volcanoes. 163 



" 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, although 

 not concentric with them, and seem to have been produced 

 after the large ones were completely closed, either by tra- 

 chytic ejection 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 com- 

 mon 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, pro- 

 bably, completely 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 ac- 

 count 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 Riphese, &c, may represent t hi formation, 

 surrounding vast basins, and having modern volcanoes fol- 

 lowing the 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 glaciers, 

 which yet possess a certainly higher temperature. Cold, 

 and other unknown causes, may have absorbed and fixed all 

 the atmosphere which anciently existed, as we see that the im- 

 mense atmosphere which anciently surrounded the earth has 

 been fixed by several chemical processes and reduced to its 

 actual composition ; and it might be possible that this ac- 

 tually existing atmosphere of ours should be all solidified, 

 either by cold or chemical processes, if the earth arrives at 

 the same degree of cold which seems to have place on the 

 moon." 



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