Page:Popular Science Monthly Volume 29.djvu/372

358 early geological times, if the same causes then existed. Whether they have been specially searched for, I do not know; but their absence, if established, would strengthen the conviction that the conditions of arctic climate which produced such a peculiar mode of growth did not exist in the time many thousand years earlier when libocedrus, magnolia, and zamia were denizens of high latitudes.

There are other facts whose tendency is in the same direction.

It is admitted by all that the climate in the earlier geological times and down to the end of the Miocene was warm through the whole year. If, therefore, the earth's axis was then inclined 23° as now, the plants of Spitzbergen and other high latitudes must have spent during every year of their existence more than four consecutive months without a ray of sunshine, and surrounded by an atmosphere moist and warm.

Their condition resembled that of plants in a warm, dark, and moist cellar. Modern vegetation so placed soon bleaches and dies. Undoubtedly it was possible for a specially adapted flora to exist under such circumstances. And a special flora is what we should expect. But the flora of Spitzbergen was not special; it was cosmopolitan in all the earlier periods, and in the Miocene some of the identical species flourished there with "amazing luxuriance," whose descendants, with specific character unchanged, are now found in the Southern States of our own country. It seems to me that this is presumptive evidence, if not demonstration, that as late as the Miocene the long arctic nights were unknown.

Moreover, this very luxuriance of foliage, which so surprised Lyell and other geologists, tends to the same conclusion. It is a matter of common observation that plants exposed to the full force of the sun's rays have smaller leaves than others of the same species which are somewhat protected. It would seem as though Nature compensated for the inferior intensity of the solar action by giving more surface to be acted upon. Now, since the intensity of the sun's rays varies as the cosine of the latitude, it is evident, in case the sun underwent no change in declination, that, while the length of the day in Spitzbergen and Florida would be the same, the intensity of the light in the latter would be almost double. Hence, if the earth's axis really was nearly or quite perpendicular, with the same conditions as to moisture and warmth, we ought to look for greater breadth and length of leaves in Spitzbergen than in regions much farther south, and we find them.

I know of but one fact in the geological record which seems to point to the existence of changing seasons. Fossil exogenous trees of very early times have been found with well-developed growth-rings, and, as these are usually attributed to seasonal changes, it has been said that they prove the existence of seasons; and, as these are due to the obliquity of the earth's axis, any inference to the contrary from other facts must be wrong. But growth-rings do not of necessity indicate