Geology first gives us an adequate conception of time.  The limitations which shut our fathers into the narrow close of six thousand years are taken down by this great science and we are turned out into the open of unnumbered millions of years.  Upon the background of geologic time our chronological time shows no more than a speck upon the sky.  The whole of human history is but a mere fraction of a degree of this mighty arc.  The Christian era would make but a few seconds of the vast cycle of the earth’s history.  Geologic time!  The words seem to ring down through the rocky strata of the earth’s crust; they reverberate under the mountains, and make them rise and fall like the waves of the sea; they open up vistas through which we behold the continents and the oceans changing places, and the climates of the globe shifting like clouds in the sky; whole races and tribes of animal forms disappear and new ones come upon the scene.  Such a past! the imagination can barely skirt the edge of it.  As the pool in the field is to the sea that wraps the earth, so is the time of our histories to the cycle of ages in which the geologist reckons the events of the earth’s history.

Through the eyes of the geologist one may look upon his native hills and see them as they were incalculable ages ago, and as they probably will be incalculable ages ahead; those hills, so unchanging during his lifetime, and during a thousand lifetimes, he may see as flitting as the cloud shadows upon the landscape.  Out of the dark abyss of geologic time there come stalking the ghosts of lost mountains and lost hills and valleys and plains, or lost rivers and lakes, yea, of lost continents; we see a procession of the phantoms of strange and monstrous beasts, many of them colossal in size and fearful in form, and among the minor forms of this fearful troop of spectres we see the ones that carried safely forward, through the vicissitudes of those ages, the precious impulse that was to eventuate in the human race.

Only the geologist knows the part played by erosion in shaping the earth’s surface as we see it.  He sees, I repeat, the phantoms of vanished hills and mountains all about us.  He sees their shadow forms wherever he looks.  He follows out the lines of the flexed or folded strata where they come to the surface, and thus sketches in the air the elevation that has disappeared.  In some places he finds that the valleys have become hills and the hills have become valleys, or that the anticlines and synclines, as he calls them, have changed places—­as a result of the unequal hardness of the rocks.  Over all the older parts of the country the original features have been so changed by erosion that, could they be suddenly restored, one would be lost on his home farm.  The rocks have melted into soil, as the snow-banks in spring melt into water.  The rocks that remain are like fragments of snow or ice that have so far withstood the weather.  Geologists tell us that the great Appalachian chain has been in the course of the ages reduced almost to a base level or peneplain, and then reelevated and its hills and mountains carved out anew.