PLATE VI. 



Pliotographed by Ritchey with 40-ltic]i telescope, using yellow color screen and isochromatic 



plate. 



This plate shows jiart of the southwest quarter of the moon's visible surface. 



On the lower part of the plate is a portion of the Mare Tranquilitatis; on the middle 

 of the left-hand side a portion of the Mare Nectaris. 



The large, deep vulcanoid with the steeji, ragged peaks rising from its floor, on the 

 lower left-hand portion of the plate, is Theoiihilus, one of the noblest structures on 

 the moon. The width of the crater is about 64 miles; the greatest height from the 

 floor to the crest of the wall, 18,000 feet. The central mass, composed of several 

 sharp peaks, rises about 6,000 feet above the lava plain. In the center of these 

 masses there appears to be an obscure crater about half a mile in diameter. The 

 terraces in the inner wall of the cone are indistinctly shown. 



Theophilus has partly invaded Cyrillus, the next large vulcanoid on the southeast, 

 an older structure with less steep slopes and a generally ruined appearance. South of 

 Cyrillus, at a distance of half its width, is Catherina. This crater is met by another 

 of half its diameter, which has developed on one side of its floor. From near the 

 southeastern margin of Catherina a beautiful row of small craters extends eastwardly 

 for a distance of over 200 miles to the large vulcanoid Abulfeda. This is perhaps 

 the most noteworthy crater row on the moon. 



The long, curved wall extending from Piccolomini, near the upper left-hand corner 

 (the large crater with its floor in shadow), to the east side of Catherina, is the Altai 

 Mountains. It should be noted that this step-like structure obscurely extends north- 

 ward to the M. Tranquilitatis, where it forms an irregular ridge-like promontory. 



