There is yet another proposition which must be established if the Age theory of Mosaic geology is to be maintained. The scheme depends essentially on the theory of central heat. We saw that Miller undertakes to account for each of the six Mosaic days or periods. As a geologist, indeed, he felt himself to be under a special obligation to explain the creative operations of the third, fifth, and sixth days, that is to say, the day on which vegetable life was created and the successive days on which different orders of vertebrate animals were introduced into the world; but he gives delineations of the prophetic vision of the first two days, and he assigns the occurrences of the fourth day, namely, the appearance of the sun and moon, to the Permian and Triassic periods. In one word, he accepted the responsibility of adapting his scheme of reconciliation to all the day-periods of Genesis, and he was perfectly aware that the hypothesis would require to be rejected if the theory of central heat were invalidated. His geological explanation of the first four days depends explicitly upon the opinion that, at the time when the earth entered upon those changes which are chronicled by geological science, it was under the influence of intense heat, and gradually cooling and solidifying. In the first day thick darkness lay upon the surface of the earth, owing to the canopy of steam, impermeable by light, under which it lay shrouded. During the second day the light began to penetrate the vapoury veil, and dim curtains of clouds raised themselves from the sea. On the third day the forests, which were heaped up for us into treasuries of coal, came into existence, and Miller accounts for their luxuriance by supposing that the heated and humid state of the atmosphere of the planet, still dependent upon the central fires, favoured their growth. It was not until the fourth day that the blanket of the ancient night was rent asunder, that sun, moon, and stars beamed out, and that a state of the atmosphere and a succession of summer and winter, day and night, identical with those we now witness, began. Possibly enough, had Miller found himself ultimately forced to abandon the theory of central heat, he would have entrenched himself, as in a second line of defence, in the three specially geological day-periods. But he never contemplated an abandonment of the doctrine of central heat. He held that the earth was once a molten mass, and that the series of changes through which it has passed arose naturally out of this fact. The crust of granite he believed to have been enveloped, in the process of cooling, by a heated ocean whose waters held in solution the ingredients of gneiss, mica-schist, hornblende-schist, and clay-slate. The planet gradually matured 'from ages in which its surface was a thin earthquake-shaken crust, subject to continual sinkings, and to fiery outbursts of the Plutonic matter, to ages in which it is the very nature of its noblest inhabitant to