At this day the scholar must be ready to explain the steps by which he reaches his conclusions. Not necessarily explaining the minutiæ of his journey hither, but the main outlines of his course. This seems to call for a slight outline of Geology. The animal and vegetable tribes which have come and gone upon the earth, following each other like the shadows of passing clouds on a Summer’s day, have left their remains in the rocks which at that time were forming. A close investigation of these remains shows that they form the record book of nature, wherein we are permitted to read somewhat of her secrets. This had long been a sealed book to man; but science, as we have seen, constantly extending her domain, at length taught him the alphabet. And the Geologist now unfolds the past age of our world with a variety of detail, and a certainty of conclusion well calculated to inspire us with grateful admiration. It is no longer a question that many ages must have rolled away, during which our world was totally unfit for life of any kind, either animal or vegetable. The nebular theory of Laplace, as modified by the modern astronomers, so satisfactorily explains many of the phenomena of the solar system, that it takes rank almost as a demonstrated fact. According to the terms of this theory, our Earth, now so dependent on the sun for light and warmth, was itself a glowing orb, and as a bright star radiated its light and heat into space. Grand conception, and probably true. It is now useless to speculate as to how many cycles of almost infinite years had begun and ended, before Earth’s fading fires gave notice that they must soon expire in night. The stages through which the Earth passed in turn await the sun, save that there is no further beneficent luminary to give him light and heat: when time shall have quenched his fiery glow, death and night shall reign supreme, where now is life and light. Time is long, and nature never hurries. She builds for infinite years, and recks not the time of building. The human mind is far too feeble to comprehend the duration of time that sped away and was gone ere the slowly falling temperature of the Earth admitted the formation of a crust over her surface. When that came, the first great scene was closed. The star had expired, the planet rolled in her annual course around the still glowing central sun. Now came the formative age of the world, when the great continents were outlined.