have landed on the earth even with greater frequency than in these latter days. But it must be admitted that in other respects the appearance of the heavens would have been totally different in the days of the ichthyosaurus from that which we now know. The Great Bear would not then have been discernible as the most striking group in the northern sky. Orion and the other well-known groups would not have yet come into vision. The pole would not then have been indicated by the pole star, and whatever may have been the brightest star in the heavens it is almost certain that it cannot have been Sirius. A zodiac there was, no doubt, but the signs by which it was to be marked were not the Ram and the Bull and the Heavenly Twins, or the other groups which have discharged that duty throughout the ages of human history. It may have been that the Milky Way was a luminous girdle around the heavens in the time of the ichthyosaurus, as it is at present. But it is certain that the general features of the heavens must have been profoundly modified between the long distant past and the present.
It may, therefore, be noted as a curious circumstance that the only permanent feature of our heavens in regard to such periods as those we are considering are not the fixed stars but the wandering planets. As they wandered then so they wander still, ever remaining members of that system over which the sun presides. It is no doubt impossible for us to form any conception as to what those stars or groups of stars may have been which adorned the skies of ancient geological times in the same way as our own constellations brighten our present skies. Calculations so instructive elsewhere will not suffice here. No methods known to us,
