These two fine examples of lunar volcanic craters are conspicuously situated in the north-east quarter of the moon’s disc. Aristarchus has a circular rampart nearly 28 miles diameter, the summit of which is about 7500 feet above the surface of the plateau, while its height above the general surface of the moon is 2600 feet. A central cone having several subordinate peaks completes the true volcanic character of this crater: its rampart banks, both outside and inside, have fine examples of the segmental crescent-shaped ridges or landslips, which form so constant and characteristic a feature in the structure of lunar craters. Several very notable cracks or chasms may be seen to the north of these two craters. They are contorted in a very unusual and remarkable manner, the result probably of the force which formed them having to encounter very varying resistance near the surface. Some parts of these chasms gape to the width of two to three miles, and when closely scrutinized are seen to be here and there partly filled by masses which have fallen inward from their sides. Several smaller craters are scattered around, which, together with the great chasms and neighbouring ridges, give evidence of varied volcanic activity in this locality. We must not omit to draw attention to the parallelism or general similarity of “strike” in the ridges of extruded matter; this appearance has special interest in the eyes of geologists, and is well represented in our illustration. Aristarchus is specially remarkable for the extraordinary capability which the material forming its interior and rampart banks has of reflecting light. Although there are many portions of the lunar surface which possess the same property, yet few so remarkably as in the case of Aristarchus, which shines with such brightness, as compared with its immediate surroundings, as to attract the attention of the most unpractized observer. Some have supposed this appearance to be due to active volcanic discharge still lingering on the lunar surface, an idea in which, for reasons to be duly adduced, we have no faith. Copernicus, in the remarkable bright streaks which radiate from it, and Tycho also, as well as several other spots, are apparently composed of material very nearly as highly reflective as that of Aristarchus. But the comparative isolation of Aristarchus, as well as the extraordinary light-reflecting property of its material, renders it especially noticeable, so much so as to make it quite a conspicuous object when illuminated only by earth-light, when but a slender crescent of the lunar disc is illuminated, or when, as during a lunar eclipse, the disc of the moon is within the shadow of the earth, and is lighted only by the rays refracted through the earth’s atmosphere.