surroundings constitute one of the most intricate regions on the moon, high plateaus alternating with great sunken valleys, rings, craters, and crater pits. The wall of Sacrobosco is extremely irregular in height, shooting up in some places with peaks of 12,000 feet elevation, and sinking in others almost to the level of the surrounding plateaus.” We now took up the next photograph representing Theophilus and its companions on a greatly enlarged scale. My friend uttered a cry of astonishment upon seeing it. “Dear me,” she exclaimed, “the moon becomes more terrible every moment! Positively, I almost shrink from the sight.” [Illustration: THE GIANT RING MOUNTAINS, THEOPHILUS AND ITS NEIGHBORS. ] “Yes,” I assented, “it surely is terrible here. In a little while, however, I shall show you a lunar scene of surpassing beauty. But study this spectacle with an inquiring mind and you will find that it, too, has its attractions. You are now looking upon Theophilus, Cyrillus, Catharina, and the surrounding region as the astronomer sees them with the most powerful telescopes. Indeed, with the telescope he sees the details more sharply than they are visible here, for the best photographs still lack something in distinctness. The illumination when this picture was taken was practically the same as in the last that we examined, but the magnification is much greater. Look, now, at the central mountain in Theophilus. Its great buttresses cast their shadows into profound ravines and chasms, imparting to it a most singular outline. Observe the tooth-shaped shadows of its two principal peaks, thrown westward across the floor, while the broad shadow of the western wall emphasizes the immense depth of the depression. The glare of the afternoon sun on the cliffs of the inner side of the eastern wall is so brilliant that the details are obscured. But the surface of the moon outside, particularly toward the north and the west, is beautifully brought out with all its wonderful modulations and irregularities. Judging by appearances, those who hold that Theophilus and similar formations, notwithstanding their enormous magnitude, are really of volcanic origin, have the strongest reasons for their opinions. Immense flows of lava seem to have taken place on all sides of the great ring, entering the _Mare Nectaris_ on the west. Notice the huge mountain fold which runs from the parallel ridges on the southwestern side of Theophilus to the crater ring Beaumont, lying west of Catharina. Observe, also, the complicated form of the wall dividing Theophilus and Cyrillus. Two deep ravines, shown by the shadows that fill them, cross one another like the arms of a flat letter X. One of these ravines turns northward along the wall and re-enters Theophilus, while the other continues for a long distance within the western side of Cyrillus. I cannot imagine a more interesting or a more stupendous excursion for a geologist, a mountaineer, or a seeker after wonderful and sublime