Page:Popular Science Monthly Volume 17.djvu/365

Rh by the phrase "the fossil man" is intended in this article man as the contemporary of certain species of animals now either totally or locally extinct, which we know only from their bones, dug out of the earth, but as to whose existence history and tradition are silent. Such animal remains are found, mingled with those of species still living; but they occur under geological conditions which show that the formerly existing surface of the earth differed in certain respects from its present state. This geological epoch, the nearest in point of time to the present, is called the Quaternary period. It is characterized by extensive deposits of rolled and water-worn pebbles, gravels, and clays, underlying the cultivable surface-soil, and due to the action of former extensive glaciers and of great and rapid currents of water. These latter were produced by the melting of that sheet of snow and ice which once covered large regions of the northern portions of Europe and America, combined with a climate much more humid than the present, and a consequent greater rainfall. This moister climate arose from a different relative arrangement of the then existing continents and seas. The general contour of the earth's surface, then, so far as existing elevations are concerned, seems to have resembled very nearly its present appearance; thus these great currents in many instances took the courses of the present river-systems in northern and central Europe and North America. The Quaternary deposits, consequently, have often been left in the neighborhood of existing streams, which now seem like shrunken rivulets in comparison with these mighty rivers of old. Through these deposits and the underlying strata the present rivers have cut their channels, leaving the Quaternary gravel-beds sometimes as high up as two hundred feet on the slopes of their valleys. In some cases oscillations of level of the surface, or other causes, have left such deposits where there are no longer existing rivers. They are, however, all characterized by similar features, and are called by geologists indifferently Quaternary gravels or drift; while the beds composed of the finer particles, often of great thickness and spread like a carpet over extensive plateaus, are named loess or brick-earth. That such beds of gravel or loess were not deposited by the sea is proved by the fact that such animal remains as occur in them are all those of land or fresh-water, and never those of marine, species.

But it is not only in the Quaternary gravels and loess that the bones of extinct animals are found; they occur more frequently in numerous caverns and fissures in the rocks. As these are met with most commonly in limestone formations, the bones are in consequence generally imbedded in or covered by a stalagmitic formation, produced by the percolation through the roof of water charged with carbonate of lime. Such a floor of stalagmite, sometimes of great thickness, covering and completely sealing up the contents of the underlying beds, is at once a proof of their antiquity and a guarantee against the possibility of such contents having become confused with objects of a later date.