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 Whether there be geological evidence bearing on the question, or whether such evidence be wanting, I do not think that the result of the laws of heat will be disputed by any one who is aware of the physical necessity which those laws impose. We can indeed cite analogical evidence from other bodies in the universe in support of our contention as to the superior efficiency of the early terrestrial volcanoes over their degenerate successors of the present day. I have already had occasion to refer to the striking if well-known fact that the lunar volcanoes are now quite extinct. The exhaustion of their primitive power is due to the circumstance that the moon is small enough to have cooled rapidly and thus to have lost almost all its internal heat. It therefore no longer retains the energy necessary for the production of volcanic outbreaks.

Here we have an instance which proves that the uniformitarian hypothesis is not satisfactory so far as lunar geology is concerned. If there were a geologist at present on the moon he would be constrained to admit that his globe was once the seat of volcanic activity of the most widespread character, and of a vehemence and potency the like of which could not be paralleled on any known globe. But while the evidence of this fact was all round him, he would be constrained to admit that his volcanoes had now lapsed into a state of permanent quiescence. So far from uniformity in volcanic matters being the characteristic of lunar geology, we find the volcanic activity of that globe gradually declining through a succession of ages until at last the present stage of absolute inertness has been reached. Uniformitarianism could not be the creed of any lunar geologist;