nor can there be a reasonable doubt that in volcanic matters our earth is progressing along a like course to that which the moon has taken.
Some of our volcanoes still retain activity, because our globe is so large that it has not yet parted with all its initial fiery vigour, but day by day the internal heat is being dissipated. We are tending from a period when the volcanoes were perhaps as important a feature on this earth as they once were on the moon; we are tending towards a period when the volcanoes on this earth shall have become as silent and as extinct as are those craters on the moon, which make our satellite so interesting a telescopic picture. The analogy of the moon will at least justify my contention that the activity of the volcanoes now on our earth is not to be regarded as adequately representing the much more terrific vehemence of the internal heat which must have devastated our globe in anterior stages of its history.
We have next to consider how the volcanic energy of these early fiery mountains on the earth can have produced sufficient explosive power to project missiles into space with a speed at least as great as that critical value to which I have so often referred. It is unfortunate that there is no globe in our solar system which can be seen to be passing at present through the same phase as that through which our earth must have passed in the early times referred to. It would have been so very instructive to have made a telescopic examination of some other world of about the same size as the earth and in about the same stage in its evolution as this globe was before the deposition of the sedimentary rocks. But there is no such globe. Jupiter does not present the conditions, for we are not
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