The general evidence of geology is familiar probably to most of us, and it is only the general evidence with which I can desire to deal on such an occasion as this; but pray observe that while the particular conclusions of geology, like those of other physical sciences, are liable to continued modification and amendment, the general drift of the conclusions is sufficiently clear and certain. No one can doubt, for instance, the great antiquity of our globe, and the fact that it has gone through successive changes with regard to the character of its surface, the nature of its inhabitants, and the like. Undoubtedly there was a time when civilized men did not dwell upon it; undoubtedly there was a still more distant period when men did not dwell upon it in any form, civilized or uncivilized; perhaps there was a period even more distant, when life was not to be found upon the earth's surface at all. And physical astronomy will take us even beyond geology, and will make it probable that the earth was originally in a fluid condition, in which from the excessive temperature no form of life could have existed. Few problems are more curious than that which deduces the present figure of our globe from the hypothesis of original fluidity. Take a mass of fluid, and set it revolving slowly about an axis, as our earth revolves, and it can be shown that it will assume such a form as that which our earth has. I do not lay stress upon the remarkable numerical coincidence of the ellipticity of the earth, as derived by Laplace from theory, with that which is discovered by observation, because this involves certain arbitrary hypotheses; but taking those results which involve nothing arbitrary at all, it is almost impossible not to believe that the earth was at one time a hot fluid mass, and that it has gradually cooled down and hardened into its present permanent condition.