the inference that the actual species of plants were tropical, for it often happens that different species of the same genus, having considerable external resemblance, are very different in their habits, some requiring tropical heat, while others flourish only in temperate climates)—­but the marked feature is the astonishing luxuriance of this vegetation, which could only have been developed under the most favourable circumstances of warmth and moisture.  Now the heat which any particular portion of the earth’s surface receives from the sun depends entirely upon the latitude. hence it is impossible that a uniform high temperature could exist in a world which derived its heat wholly or chiefly from that source.  Whether the high temperature which prevailed on the earth during the deposition of the coal measures was derived from internal heat it is impossible to say; it is evident that the temperature of the earth’s surface has been in past times, and perhaps is now, modified by causes which no scientific research has been enabled to detect [Footnote:  Since the sun’s secular motion has been known, astronomers have suggested that the solar system has been carried through portions of space having variable temperatures.  Geologists, however, do not seem inclined to accept this as a sufficient reason for the phenomena observed.].  But we may safely conclude that during the third day the earth did not derive its heat from the sun.  The second point, the barrenness of the geological records of this period, will be noticed hereafter.

The record of the fourth day’s work admits of two interpretations, it may describe things merely as they appeared, or as they actually occurred.

1.  It is possible that the events of the fourth day may be described phenomenally—­that up to this period the state of things on the earth had been to a great extent similar to that which we have reason to believe is still existing in the planet Jupiter-that the atmosphere was so charged with vapour that no direct rays from the heavenly bodies could penetrate it; but that at this time, owing to the declining heat, a great part of the aqueous constituents of this vapour had been precipitated in the form of rain, while other vapours had entered into chemical combinations with other elements to form the various minerals of the earth’s surface, and the atmosphere had become first translucent, and then transparent.  While this process was going on, no direct light from the sun, supposing it to be already in existence, could penetrate the veil.  Diffused light only could reach the earth’s surface, but when the atmosphere became clear the sun, moon, and stars would become visible.