early oceans and seas, what shrimps and crabs are to ours. They are supposed to have swum at the surface of the open sea, feeding on their marine companions, and to have been able to roll themselves into a ball, so as to defend themselves when threatened with similar consequences. Their mode of locomotion was either by means of soft paddles or the flexible power of the body. But the eyes, which have been preserved in some of these fossils, are the most wonderful in their organization, and form a feature most interesting for the geologist. Dr Buckland observes" This point deserves peculiar consideration, as it offers the most ancient, and almost the only example yet found, in the fossil world, of the preservation of parts so delicate as the visual organs of animals that ceased to live many thousands, and perhaps millions of years ago." There are two eyes, each consisting of 400 compartments or lenses, so placed on the surface of the cornea, projecting conically upwards, that they all look outwardly from the animal's head. These, then, are raised so that the animal, from its position at the bottom of the waters, can see all around without any hinderance from its own protuberant body; but their inward lines of vision do not cross each other, as that would have been an unnecessary waste of power-a striking instance of the combination of fertility and economy that nature so often loves to present unto us. Wealth, not waste, seems ever her motto. But the Trilobite has been a means of important special instruction to the geologist. It tells that the air, the light, and the sea waters of the incalculably distant eras, when the Trilobites flourished in such amazing profusion, were essentially as they are now. For, first, if the deep waters had been turbid, such delicate organs of vision would have been useless; second, had the atmosphere differed from its present condition, the rays of light would have been also affected to a different result, and then we should not have found, as we do find, the eyes of existing Crustaceans agreeing with the older Crustaceans in question; and, thirdly, as to the light itself, it is certain that the mutual relations of light and optical vision were essentially the same as now, because the essential organizations of the eye in both periods are the same, a happy instance of sound logical and geological deduction. How wonderful, how awful, to think that we can thus, as it were, arrive at that period in the backward history of the world when air and water enclosed it in their embrace, and light itself first burst upon the scene! How comforting to see that the Divine being then exercised a care and solicitude for the well-being of His creatures as great as He has now for those of later ages; "God, the same yesterday, to-day, and for ever." Even in this stage of life the distinction, with which we are familiar, existed between the vegetable feeders and the flesh eaters. The Trilobites belonged to the Carnivora, the latter class. "What sea receding from what former world Some geologists have imagined that dry land, to some extent, prevailed during the Silurian age, and they do so upon the ground that great disintegration is exhibited in the strata. While it is no doubt true that greater disintegration takes place where land and water meet than under the ocean, it must be borne in mind that disintegration must have been produced by volcanic action, beneath the water, in a greater degree by far than by atmospheric action. That, towards the close of the Silurian age, the internal forces were not quiescent, is evidenced by the displacement of the strata from their original and horizontal position, and the masses of igneous matter, such as lava, greenstone, serpentine, and porphyry, which have been forced upwards, and flowed in rivers of molten materials in every direction. The economy of nature has ever been the same in regulating the proportion of creatures by the supply of food for their subsistence. No remains of land plants have been discovered. The epoch presents our world covered by a shoreless sea, inhabited by invertebrate animals the Zoophytes, imbedded in the muddy bottom; the Star-lillies on their stems, waving their tentacles in search of their prey; the Trilobites and Molluscs, equally voracious, roaming in every direction. Towards the conclusion of the period, traces of vertebrate animals in fishes appear, but no bird was there to break the monotone of the ceaseless wave with even the faintest twittering note; not an insect to dot the sunbeam with its tiny wing; no reptile, no mammal, not a single flower or plant or leaf, to catch a single drop of dew. Yet life in its lowliest form had received its beginning, through succeeding ages and formations to increase in extent and wondrous form, only to culminate in perfection and to inhabit eternity. The deposition of the strata we have been describing, although of immense extent, yet, compared with the size of the earth, holding but the proportion of the paper which covers a twelve inch globe to the body which it covers, no doubt retarded considerably the radiation into space of the heat of the earth itself; and ages must have passed, during which thousands of generations of Crustaceans, Molluscs, and Zoophytes lived and died, providing, by means of their shells, immense quantities of carbonate of lime. This quiet and systematic order of things was stopped by great and terrific convulsions of nature, arising from the contraction of the fluid mass of the earth, occasioned by its cooling from the radiation of heat into space; and the crust thus contracted appears to have given way over almost the whole surface of the globe, producing rents, and fractures, and dislocations of the whole stratification, primary and transition. Volcanic action, too, of the most tremendous character, seems to have accompanied these disturbances, and, in combination with the meeting, in opposite directions, of the surging waves of the sub-existing fluid matter, to have resulted in the elevation of those mighty mountain ranges of the existing world, which now lift their snowcapped tops above the clouds. These rugged and peaked tops are formed of the fractured masses of the broken strata, thrust upwards, borne to their aërial resting places on the crests of the opposing waves of molten earth. The mighty volcanic, and other convulsions, induced another change, by diffusing iron oxides into the waters, and changing the sediment, formerly a dark grey mud, into a red tinge. No doubt, also, it exercised fatal effects upon the then inhabitants of the sea, for many species then disappear from the roll of life, CHAPTER V. THE causes noticed in the last chapter having subsided, the surface of the earth assumed a new arrangement, and the Devonian era was ushered in by the deposition of the secondary strata, around the ranges of the primary rocks, and in the hollows and undulating bed of the sea, by the same processes of disintegration of the primary strata, and the operation of the same agencies of transport, deposition, and condensation. The secondary strata comprises the Old Red Sandstone, so called from its deep red colour, as exhibited in Devonshire (where it is most abundant, and hence sometimes named Devonian, and to distinguish it from the New Red Sandstone found above the Coal measures), the Mountain Limestone, and the Coal measures. Its entire thickness is small, as compared with the preceding systems, and it extends over much less space, but it is far superior to them in all that concerns the development and support of organized beings. The composition of the Old Red Sandstone is very varied, alternating from rocks of the finest grain, and laminated, to conglomerate of sand and pebbles, of varied colours, from red to yellow. The whole are evidently aqueous deposits, and many of the strata exhibit the ripple marks of the ocean waves of countless ages bygone, as clearly as the sand of the beach |