M. Chacomac on the Moon. 373 



turn has moulded itself upon the cavities of the more ancient 

 eruptions. 



As types of each of these forms, completely different and 

 characteristic of successive epochs of formation, we may refer 

 to Herschel or Alpetragius, and Ptolemceus. These show 

 especially the ordinary diminution of magnitude of the more 

 recent as compared with the buried craters. In fact, the dia- 

 meter of Ptolemceus is more than forty, while that of Herschel 

 is less than four leagues, although the height of the eruptive 

 cone of the latter is more than 200 metres higher than the 

 loftiest peak of Ptolemceus ;* while the minute exploration of 

 the " sea-shores " proves that in all cases where the continen- 

 tal ground has offered an accessible opening, an influx has 

 taken place from without, and the adventitious material has 

 risen there to the general level which it preserves [sufficiently, 

 at least, for the present argument] throughout the visible 

 hemisphere. 



Among the numerous results of this kind of general clilu- 

 vhim, we discover, in an immense number of points on the 

 plains, evidence of the subsequent levelling of igneous products ; 

 and these levellings are the more distinguishable for three rea- 

 sons : the continents have a much greater reflective power than 

 the maria ; their relief is usually very marked and sharp ; and 

 their structure, whether as mountains or craters, always has a 

 circular type and a scoriaceous consistency ; while, on the other 

 hand, the slight protuberances of the 'maria are merely oblong 

 hills of slight elevation, and uniform [general ?] rectilinear 

 direction. The configuration of these hills, whose material is 

 exactly similar to that of the plains, is perfectly comparable to 

 the ridges of sand thrown up by our tidal waves on broad, 

 sandy beaches. The linear shape of these slight undulations, 

 together with the difference of their structure, leaves no doubt 

 as to the nature of the emergent spots, marked by strong 

 relief and sharp outlines, which occur scattered in the centre 

 of the lunar oceans. 



Among other characteristics of the primitive surface, we 

 notice immense rings, whose crests alone project above the 

 surrounding plain by some hundreds of yards — circular ram- 

 parts, the last visible vestiges of great buried craters : and 

 these are cut through by considerable breaches, which permit 

 us to follow the level of the maritime soil where it penetrates 

 their interiors, and to remark the absence of the slightest 

 difference in surface or structure. We might suppose that we 

 were looking upon the remains of an archipelago similar to the 

 Phlegrean Fields, invaded by a fluid but subsequently conso- 



* The French league is very nearly equal to 2§ English, miles. The French 

 metre is 3 feet 3*37 inches, English measure. 



