The Eozoon. discovered in the upper or later Laurentian, the fossil of an animal, Eozoon (dawning life), so simple and yet so obscure in structure, that its organic character is still in some doubt. If it is an animal, as it probably is, it is of the very lowest form, one of the minor Protozoans. Life began at the lowest point, and with the simplest mode of growth. Here, then, we find the introduction of life upon the earth, in the form of plants, and possibly of animals also. The occurrence of limestone and beds of iron ore in the same formation are also regarded as signs of the existence of some kind of life, since these owe their origin chiefly to organic agency. But little account has yet been made of this fact by the geologist, however, in dealing with the Laurentian rocks. The Silurian formation. We now move up one step in the series. Next in order after the Laurentian came the Silurian rocks, so named from a district in England where they show at the surface. They are made up of successive series of beds of sandstone, limestone, and shale (a soft irregular slate), nature having now got fairly to work, wearing away rocks, transporting the abraded material by means of wind and ocean currents, and building them up in other places. We find in these rocks the remains of both plants and animals, many still of low type and very simple structure, such as the sea-weed among plants and the sponge and coral among animals; but there are found also both plants and animals of higher forms and more varied constitutions, showing a great advance over the life of the former period. The Radiates doubtless existed in great numbers, especially corals and crinoids, or flower animals, as they are sometimes called by reason of their peculiar shape; but as they are fragile or pulpy in substance, and therefore easily destroyed, they do not appear in great numbers in the rocks. But the Mollusk, with his strong shell to protect him in life and keep his memory alive when he is dead, appeared in strong force, and some beds of the Silurian rocks, as those which appear at Trenton Falls, New York, are composed almost wholly of its remains. To walk along the shelving banks of that stream (Canada Creek), or on portions of its dry bed when the water is low, as it is sometimes late in summer, is to tread upon millions of skeletons or casements of these animals that lived in the sea in the Silurian age. This formation, extending eastward into Vermont, was metamorphosed or crystallized in the upheaval of the Green Mountains, and constitutes the extensive marble beds of that region. The Green marble. There was as yet little if any life upon the land. The ocean was inhabited-the scene, perhaps, of strife and depredation; the land was almost utterly bare and still. Plants of the Silurian age. The plants of this period either did not advance so rapidly, or, as seems more probable, their softer substance rendered them more liable to destruction in the geologic convulsions and revolutions that marked, at that early day, the changes from one period to another. What plants do reveal themselves, however, show a considerable variety, including a large number of marine plants and in the upper layers a few that grew on the land. Some additions have been made by recent explorations, and others may still be added to the list. The whole number of plants that can be identified is small in comparison with the number of animals, and they are chiefly if not entirely of the class of Acrogens. This difference in number is nothing remarkable, however, considering the readiness with which tender herbage yields to the action of the elements. The Leaving now the Silurian we pass next to the Devonian formation, named also from an Devonian English district. Hugh Miller styled it the "Old Red Sandstone." And here we shall find some marked changes in of life among both animals and plants. formation. the types First the plants were much more numerous; or if not more numerous in growth, then more successfully preserved in fossil. They belong chiefly still to the first class of plants, though one or two, of higher but uncertain type, have been identified. It must be borne in mind that the extent of sea was much greater than at a later period, and that of land correspondingly less. And this may account for the fact that the plants continued of that class that flourishes best in the sea, or in immediate proximity to it. The higher plants require high and comparatively dry land. But the animal life of the Devonian period was abundant and varied. Not only did the Mollusks hold a place, as to numbers, almost equalling that of their Silurian congeners, differing merely in slight structural details, attaining perhaps something more of symmetry and something more of distinctive character; and the Radiates, especially corals, multiply and extend with great rapidity and contribute their short-lived skeletons to the forming rocks, and the Articulate-insect-begin to wing its way upon the humid air, but the fish also appeared, which, having a backbone, belongs to the highest class of animals, the Vertebrates. The latter were of considerable variety and vast numbers, insomuch that the period is known in geology as the Age of Fishes. It was evidently Age of also a time of depredation and reprisals among these denizens of the deep. And many of them were amply equipped for the fray. They had coats of mail, consisting of thick bony plates,, with carapace, like a shield about the head, and sharp spike-like teeth that not only fitted them for self-defence, but must have made them the terror of their less securely armored neighbors. But such is the way of animal life. The stronger subsist upon the weaker. And but for their prodigious rapidity of increase, "bringing forth abundantly," the tribes of smaller animals would long ago have disappeared. What is lost in one way, however, is gained in another, and nature is never defeated of her ends by any casual contingency. We move now one step farther upward in the scale. The coal period. Next in order above the Devonian rocks comes the Carboniferous system, including the extensive coal formations which supply so important a necessity to-day. In this period the development of plants was most remarkable, both as to numbers and variety. Hitherto we have found very few higher than the first and lowest class. In the coal period this division still held the leading place. They grew to enormous size, and formed rank and tangled |