372 M. Chacornac on the Moon. 



buried beneath the maritime soil ; and, besides these, we find, 

 at the line of junction of the two kinds of surface, very curious 

 appearances of " erosion" and submersion of the shore, per- 

 fectly analogous to that of the Island of St. Paul, in the Indian 

 Ocean. To render this more intelligible, we may remark a 

 characteristic distinction between the usual form of the lunar 

 and the terrene crater. The latter generally occupies the top 

 of a conical mountain, and the bottom of the cavity is never 

 far beneath the summit ; the depth of the crater being only a 

 small fraction of the height of the mountain. On the con- 

 trary, the bottom of the lunar crater, in its original condition, 

 is always deeply depressed below the level of the soil on 

 which the cone of eruption is raised, so as to give it, when of 

 small dimensions, some analogy with a vast conical well. In 

 studying, for instance, those of not more than 300 to 1000 

 yards in diameter, and having a continuous ring, we come to 

 the conclusion that this is the result of a single explosion, 

 which raised the surface in the form of a bubble, and deposited 

 it round the orifice of eruption. But, to return to the pheno- 

 mena of encroachment to which such formations have conduced, 

 we find on the " sea- shores," and especially where the higher 

 ground sinks by a gradual declivity, the interiors of certain 

 partially-destroyed rings filled up by a compact mass of alluvial 

 soil, precisely as the bottom of the crater in the Island of St. 

 Paul is now invaded by the ocean. In such cases the shore 

 takes the form of a vast semicircular bay, whose entrance is 

 partly obstructed by the remains of the ring, exactly as is the 

 case with the terrestrial volcano in question. In examining 

 these extremely striking and interesting details, we shall meet 

 with what may be compared to marshy formations, immense 

 partial inundations, the complicated particulars of which are 

 not within the compass of this sketch : these marshy forma- 

 tions consist principally of volcanic hills, whose bases are 

 covered by sedimentary soil; but the most important fact 

 connected with them is the presence of other neighbouring 

 craters, which, though on the same level, are entirely empty, 

 with outlines usually unbroken, and interiors excavated con- 

 siderably beneath the marine surface, affording a singular 

 contrast to the ruined aspect of the buried craters. The one 

 have nothing left standing but the thickest portion of their 

 ramparts, and projections bearing the marks of erosion; the 

 ejections of the other exhibit themselves regularly around the 

 cone of eruption as currents of lava, preserving the smallest 

 details of their edges, and winding and spreading along the 

 shallow depressions of the plains : so that it is perfectly evident 

 that these latter craters have been formed subsequently to the 

 consolidation of the ground which supports them, and which in 



