874 M. CTiacornac on the Moon. 



lidated mass. We may refer to the two rings,, Kies and 

 liubiniezky , as curious types of this formation. Each of them 

 has ramparts of about forty-five leagues, rising sharply in the 

 midst of an immense desert to a height of two or three hun- 

 dred yards. 



It is known that while some craters exhibit only a simple 

 cavity, others possess a central peak. We may further remark 

 that in the heart of the continents flat-bottomed craters exist, 

 the peaks of which, half-emergent from the sedimentary mass, 

 demonstrate that the craters have been invaded by maritime 

 soil; and we may notice cases where all traces of central peaks 

 have disappeared beneath thick beds of deposited matter. 



To give an idea of the gigantic proportions which charac- 

 terize this kind of formation peculiar to our satellite, M. 

 Chacornac specifies the crater Schikard, lying towards the 

 S.E. limb ; the interior, which is upwards of sixty-five leagues 

 in diameter, would have to a spectator in the centre the 

 aspect of a boundless desert ; as the speedy rounding-off of so 

 small a globe would depress the rampart out of sight in every 

 direction, though attaining on the N. a height of more than 

 10,500 feet. 



After this brief examination, it remains to point out a fact 

 enabling us to class the craters of different dimensions in a 

 chronological succession. In a great number of craters such as 

 we have just described, we find that a portion of their bulwarks 

 has disappeared from the effects of subsequent eruptions, whose 

 foci have broken out even through the ring itself, and pro- 

 duced craters, usually entirely empty; and the more recent date 

 of these outbreaks is also proved by there being no trace of the 

 destroyed portion of the ring, while the ejected products of 

 the more modern are superimposed on those of the earlier 

 crater. The dimensions, also, of the encroaching basin are 

 always inferior to those of the original cavity. This, which is 

 characteristic of the lunar formations, may be considered as a 

 general law [almost ?] without exception. 



We may distinguish, then, three clearly marked selenolo- 

 gical epochs. The primitive is that during which immense 

 vesicular upheavings have given rise to crater-like rings of 

 more than 300 leagues in compass, and around which we per- 

 ceive clear traces of entangled circumvallations [circonvallations 

 enchevetrdes] . To this period would have succeeded that of a 

 general diluvium, forming deposits analogous to the alluvial 

 strata of the earth. This effusion has buried, under a brown 

 mass, more than two-thirds of the visible surface of the moon, 

 including the interiors of all the great craters, displaying itself 

 from one extremity of the hemisphere to the other, apparently 

 on the same level. Subsequently to this second period came 



