THEOPHILUS. 97. CYRILLUS. 96. CATHARINA. 95. These three magnificent craters form a conspicuous group. Their diameters and depths are as follows: Theophilus, diameter, 64 miles; depth of interior plateau from summit of crater wall, 16,000 feet; central cone, 5200 feet high; Cyrillus, diameter, 60 miles; depth of interior plateau from summit of crater wall, 15,000 feet; central cone, 5800 feet high; Catharina, diameter, 65 miles; depth of interior plateau from summit of crater wall, 13,000 feet; center of plateau occupied by a confused group of minor craters and debris. Each of these craters is full of interesting details presenting in every variety the characteristic features of the lunar volcanoes and giving unmistakable evidence of the tremendous energy which at some remote period piled up such gigantic formations. The intrusion of Theophilus within Cyrillus shows that it is of more recent formation than the latter. The flanks of Theophilus, especially on the west side, are studded with apparently minute craters. These would be considered of great size but for the enormous crater so near. PTOLEMY. 111. ALPHONS. 110. ARZACHAEL. 84. The portion of the moon's surface which includes these features, being near the center of the lunar disc, is exceptionally well placed for observation. Within this area may be seen every variety of volcanic craters and a number of other interesting forms. Ptolemy belongs to the class of walled plains, its ramparts enclosing a plain 86 miles in diameter. Alphons and Arzachael are respectively 60 and 55 miles in diameter. They have all the distinctive features of lunar craters, viz:--central cones, lofty, ragged ramparts, manifestations of landslip formations in the great segmental terraces within their ramparts and minor craters interpolated within their plateaus. A notable object near Alphons is an enormous straight cliff traversing the diameter of a low, ridged, circular formation. This great cliff is 60 miles long and from 1000 to 2000 feet high. It is a well known object to lunar observers and has been termed "The Railway" on account of its straightness. The existence of this remarkable cliff appears to be due either to an upheaval or a down-sinking of a portion of the surface of the circular area across whose diameter it extends. TYCHO. 80. This magnificent crater is 54 miles in diameter and upwards of 16,000 feet deep from the highest ridge of the rampart to the surface of the plateau. It is one of the most conspicuous of lunar craters, not so much on account of its dimensions as from its occupying the great focus of disruption from whence diverge those remarkable bright streaks many of which may be traced over 1000 miles of the moon's surface. The interior of the crater presents striking examples of the concentric, terrace-like formations that are regarded as formed by landslips.