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_."

Although, as already remarked, it seems necessary to assume that any
life existing in the moon prior to its great volcanic outburst must have
ceased at that time, yet the possibility may be admitted that life could
reappear upon the moon after its surface had again become quiet and
comparatively undisturbed. Germs of the earlier life might have
survived, despite the terrible nature of the catastrophe. But the
conditions on the moon at present are such that even the most confident
advocates of the view that the lunar world is not entirely dead do not
venture to assume that anything beyond the lowest and simplest organic
forms--mainly, if not wholly, in the shape of vegetation--can exist
there. The impression that even such life is possible rests upon the
accumulating evidence of the existence of a lunar atmosphere, and of
visible changes, some apparently of a volcanic character and some not,
on the moon's surface.

Prof. William H. Pickering, who is, perhaps, more familiar with the
telescopic and photographic aspects of the moon than any other American
astronomer, has recorded numberless instances of change in minute
details of the lunar landscapes. He regards some of his observations
made at Arequipa as "pointing very strongly to the existence of
vegetation upon the surface of the moon in large quantities at the
present time." The mountain-ringed valley of Plato is one of the places
in the lunar world where the visible changes have been most frequently
observed, and more than one student of the moon has reached the
conclusion that something very like the appearances that vegetation
would produce is to be seen in that valley.

Professor Pickering has thoroughly discussed the observations relating
to a celebrated crater named Linne in the _Mare Serenitatis_, and after
reading his description of its changes of app