I may note in conclusion, that while on the one hand we cannot doubt that the earth is slowly parting with its internal heat, and thus losing century by century a portion of its Vulcanian energy, such phenomena as the Peruvian earthquakes show that the loss of energy is taking place so slowly that the diminution during many ages is almost imperceptible. As I have elsewhere remarked, “When we see that while mountain ranges were being upheaved or valleys depressed to their present position, race after race and type after type lived out on the earth the long lives which belong to races and to types, we recognize the great work which the earth’s subterranean forces are still engaged upon. Even now continents are being slowly depressed or upheaved, even now mountain ranges are being raised to a different level, table-lands are being formed, great valleys are being gradually scooped out; old shore-lines shift their place, old soundings vary; the sea advances in one place and retires in another; on every side nature’s plastic hand is still at work, modelling and remodelling the earth, and making it constantly a fit abode for those who dwell upon it.” _STRANGE SEA CREATURES._ “We ought to make up our minds to dismiss as idle prejudices, or, at least, suspend as premature, any preconceived notion of what _might_, or what _ought to_, _be_ the order of nature, and content ourselves with observing, as a plain matter of fact, what _is_.”—Sir J. HERSCHEL, “Prelim. Disc.” page 79.