This is only one example among hundreds, scattered all over the moon, which show how the surface of our satellite has suffered upheaval after upheaval.  It is possible that some of the small craters, not included within the walls of the greater ones, may represent an early stage in the era of volcanic activity that wrecked the moon, but where larger and smaller are grouped together a certain progression can be seen, tending finally to extinction.  The internal energies reached a maximum and then fell off in strength until they died out completely.

It can hardly be supposed that the life-bearing phase of lunar history—­if there ever was one—­could survive the outbreak of the volcanic cataclysm.  North America, or Europe, if subjected to such an experience as the continental areas of the moon have passed through, would be, in proportion, worse wrecked than the most fearfully battered steel victim of a modern sea fight, and one can readily understand that, in such circumstances, those now beautiful and populous continents would exhibit, from a distance, scarcely any token of their present topographical features, to say nothing of any relics of their occupation by living creatures.

There are other interesting glimpses to be had of an older world in the moon than that whose scarred face is now beautified for us by distance.  Not far from Theophilus and the other great crater-mountains just described, at the upper, or southern, end of the level expanse called the “Sea of Nectar,” is a broad, semicircular bay whose shores are formed by the walls of a partially destroyed crater named Fracastorius.  It is evident that this bay, and the larger part of the “Sea of Nectar,” have been created by an outwelling of liquid lavas, which formed a smooth floor over a portion of the pre-existing surface of the moon, and broke down and submerged a large part of the mountain ring of Fracastorius, leaving the more ancient walls standing at the southern end, while, outlined by depressions and corrugations in the rocky blanket, are certain half-defined forms belonging to the buried world beneath.

Near Copernicus, some years ago, as Dr. Edward S. Holden pointed out, photographs made with the great Lick telescope, then under his direction, showed, in skeleton outline, a huge ring buried beneath some vast outflow of molten matter and undiscerned by telescopic observers.  And Mr. Elger, who was a most industrious observer and careful interpreter of lunar scenery, speaks of “the undoubted existence of the relics of an earlier lunar world beneath the smooth superficies of the maria.”