But the subject of footprints carries us farther back than the ages of the great historic founders of religion. In almost every part of the earth footprints have been found, cut in the solid rock or impressed upon boulders and other stones. These artificial tracks, like the strange human footprint which Robinson Crusoe discovered on the beach of his lonely island, excite the imagination by their mystery, and open up a vista into a hitherto unexplored world of infinite suggestion. They seem the natural successors of those tracks of birds and reptiles on sandstone and other slabs which form one of the most interesting features in every geological museum; the material on which they are impressed having allowed the substantial forms of the creatures themselves to disappear, while it has carefully preserved the more shadowy and incidental memorials of their life. The naturalist can tell us from the ephemeral impressions on the soft primeval mud, not only what was the true nature of the obscure creatures that produced them untold ages ago, but also the direction in which they were moving along the shore, and the state of the tide and the weather, and the appearance of the country at the time. But regarding those literal human "footprints on the sands of time," which have been left behind by our prehistoric ancestors, we can make no such accurate scientific inductions. They have given rise to much speculation, being considered by many persons to be real impressions of human feet, dating from a time when the material on which they were stamped was still in a state of softness. Superstition has invested them with a sacred veneration, and legends of a wild and mystical character have gathered around them. The slightest acquaintance with the results of geological research has sufficed to dispel this delusion, and to show that these mysterious marks could not have been produced by human beings while the rocks were in a state of fusion; and consequently no intelligent observer now holds this theory of their origin. But superstition dies hard; and there are persons who, though confronted with the clearest evidences of science, still refuse to abandon their old obscurantist ideas. They prefer a supernatural theory that allows free scope to their fancy and religious instinct, to one that offers a more prosaic explanation. There is a charm in the mystery connected with these dim imaginings which they would not wish dispelled by the clear daylight of scientific knowledge. In our own country, footmarks on rocks and stones are by no means of unfrequent occurrence. Some of them, indeed, although associated with myths and fairy tales, have doubtless been produced by natural causes, being the mere chance effects of weathering, without any meaning except to a geologist. But there are others that have been unmistakably produced by artificial means, and have a human history and significance.