In turning our attention to these features, we are at the outset struck with the paucity on the lunar surface of extensive mountain systems as compared with its richness in respect of crateral formations; and a field of speculation is opened by the recognition of the remarkable contrast which the moon thus presents to the earth, where mountain ranges are the rule, and craters like the lunar ones are decidedly exceptional. Another conspicuous but inexplicable fact is that the most important ranges upon the moon occur in the northern half of the visible hemisphere, where the craters are fewest and the comparatively featureless districts termed “seas” are found. The finest range is that named after our Apennines and which is included in our illustrative Plate, No. IX. It extends for about 450 miles and has been estimated to contain upwards of 3000 peaks, one of which—Mount Huyghens—attains the altitude of 18,000 feet. The Caucasus is another lunar range which appears like a diverted northward extension of the Apennines, and, although a far less imposing group than the last named, contains many lofty peaks, one of which approaches the altitude assigned to Mount Huyghens while several others range between 11,000 and 14,000 feet high. Another considerable range is the Alps, situated between the Caucasus and the crater Plato, and reproduced on Plate XIV. It contains some 700 peaked mountains and is remarkable for the immense valley, 80 miles long and about five broad, that cuts it with seemingly artificial straightness; and that, were it not for the flatness of its bottom, might set one speculating upon the probability of some extraneous body having rushed by the moon at an enormous velocity, gouging the surface tangentially at this point and cutting a channel through the impeding mass of mountains. There are other mountain ranges of less magnitude than the foregoing; but those we have specified will suffice to illustrate our suggestions concerning this class of features. [Illustration: PLATE XV. MERCATOR & CAMPANUS.] We remark, too, that there is a prevailing tendency of the ranges just mentioned to present their loftiest constituents in abrupt terminal lines, facing nearly the same direction, the reverse of that towards which they are carried by the moon’s rotation; and as they recede from the high terminal line, the mountains gradually fall off in height, so that in bulk the ranges present the “crag and tail” contour which individual hills upon the earth so frequently exhibit.