Probable Landscape in the Carboniferous Age. About the Time Coal Was in the Making. (After Patonie) 1. Tree fern 2. Giant ancestors of our horsetails. 3 and 4. Ancestors of our club mosses. 5. Cordaites, a primitive type, or perhaps even the ancestor of our modern evergreens. At this time no herbs and no plants with petals, were known, nor for ages after this period. (Courtesy of Brooklyn Botanic Garden.)
At the end of this period an event of commanding interest occurred, because it happened only some 40,000 years ago. With it came the encroachment from the north and south poles of the last of the great continental glaciers. There had been many before, stretching over a past period of time, but as the last of these great ice invasions it is the most interesting to us. It crowded all these temperate and even subtropical plants that then grew up in the far north toward the equator, and scraped clear of vegetation every part of the earth which it covered. In the volume on geology you will find an account of the extent and thickness of this great ice sheet, which ultimately receded to its present home. As it went back the plants crowded forward to occupy the freshly released land, the far northern or glacial first, followed by waves of other kinds. Some of the glacial or northern plants were left on the tops of the highest mountains, where to-day they persist in complete isolation, nearly all their friends and associates of that greatest of all winters having left them for points farther north. Many students of plant geography think that wave of plant life creeping northward to occupy the region uncovered by the retreating ice is still going on, and recent studies appear to show in at least one isolated mountain in the Adirondacks that the survivals of the ice age which have been isolated on its rocky peak ever since are in considerable danger of being crowded out by invaders from the lowlands.
Not all the geological changes which have remodeled the earth’s surface have been mentioned in this brief history of those plants that preceded our own, nor have anything like all the plants occurring in the different strata been even hinted at. But the thing which has been stressed and for us to fix in our minds is that all our present vegetation literally has its roots deep down in the earth. Some, as Lycopodium Selago, go back no one knows how many millions of years; others, like the flowering herbs, are much more recent. We come to understand how recent we are and what a comparatively brief flash in the pan all our modern development both of plants and in man has been since the last glacial period only by looking for a moment at what has happened in the past. In the account of the Carboniferous plants we found that there remained after that period only about 19 per cent of the earth’s age in which all the changes since then could have come about. If, as may well be possible, this period has been about 19,000,000 years, then the mere 40,000 years since the last Ice Age seems a brief period indeed. As some one has written, to contrast all man’s historic period, back to the days of the most ancient Chinese manuscript, with that long journey from the dim past which the plant world has slowly accomplished, is to realize that we are “as the flashing of a meteor through the sea of night.”
Fossil plants then, and this delving into the dead past of the plant world, reveals to us as nothing else can how much the modern plant kingdom is literally built upon a mighty race of ancestors. Some perished as did the Cordaitales, but left descendants who themselves gave rise to other groups that survive to-day. To look over a list of the fossil plant genera of the different strata is to visualize a drama the like of which no one living will ever see replayed, the results of which are recorded all over the world with its changing panorama of vegetation.