THE MOON 345 



SCULPTURE. The peculiar plateau of Wargentin and Phoc- 

 lydes are striking examples in more than one sense of some 

 tremendous lava deluge. The first-named object is a smooth, 

 nearly circular mesa 54 miles across and filled nearly to the level 

 of the lowest point of its rim with solidified lava. That War- 

 gentin does not reign alone in his unique grandeur is proclaimed 

 by the partial filling of Gassendi, Letronne and Hippalus to the 

 north; craters which experienced a community of origin with 

 Wargentin and the neighbouring depressions. 



As the result of moonlet impacts in the adjacent maria and 

 the fall of lithic dust from their conflagrations, Boscovicfi is 

 scarcely to be recognized as a crater, while Julius Caesar and 

 LeMonnier have nearly lost their characters. To the vaporization 

 of the more massive bodies the many "ghost craters" on the moon 

 owe their partial eff acement, typified by Fra Mauro, Fracastorius 

 and Cassini. As Doctor See wrote concerning these dim spectres 

 of the desolate lunar Hades: "So far as one can see, only two 

 explanations are tenable: i. The deposit of cosmical dust from 

 the heavens, and from conflagrations arising in the impact of 

 satellites. 2. The partial melting down of the walls by the 

 conflagrations which produced the maria, so that only an outline 

 of the original crater walls can be traced." 



The southern boundaries of the great Imbrian lava deluge 

 visioned forth as occurring far down the vista of the ages were 

 determined by Pitatus and Hippalus, while southwestward the 

 onslaught of the impacting planetoid's molten flood attained 

 Posidonius and eastward it lost itself in the Oceanus Procellarum. 

 By this memorable world-wide cataclysm, which at one stroke 

 wrought the Maria Imbrium, Nubium and Humorum and the 

 encricling ramparts known as the Apennine and Caucasus ranges, 

 "were introduced the features necessary to a broad classification 

 of the lunar surface." 



LUNAR "VALLEYS". A veritable "Valley of the Moon" is the 

 Rheita Valley. This is a shallow groove of varying width with 

 a shorter off-shoot on the south end. It runs from the eastern 

 edge of the crater Rheita southwestward more than 185 miles 

 to Rheita d; its breadth varies from n to 25 miles, with a maxi- 

 mum depth, according to Beer and Madler, of about 11,000 feet. 

 A long, narrow cleft resembling a rill, starts from near Picco- 

 lomini and trends southwestward more than 450 miles to near 

 Metius, which temporarily interrupts it ; but it continues its course 

 beyond that crater and to the right of the Rheita Valley. 



However, the Alps Valley, a straight defile traversing the 

 lunar Alps range, is the most interesting of them all, betraying 

 an exceptional character which demands for its origin an excep- 

 tional explanation. A trough-like flat-bottomed groove trending 

 east-north-east by west-south-west clean across the Alps range; 



