First appearance on the Globe of Land Animals.-With some such feeling as Robinson Crusoe gazed upon the unknown footsteps in the sand of his desert island did geological observers behold the mysterious marks shown in the above engraving, which were found impressed upon certain pieces of sandstone in some of the Coal measures of America within the last few years. Up to the time of these discoveries the animal life of the era appeared to be confined, as before, to the limits of the marine world, and that life on a greatly reduced scale, as regards abundance. Some estuary shells, some also belonging to the depths of the sea, a few species of fishes, chiefly Sauroids (found in the shales of the system), developed in certain cases to an enormous size-this was nearly all. As to the zoophytes and crinoidea, which were so abundant in the preceding mountain limestone, they had now altogether disappeared.

Some faint traces, it is true, had been lighted on at last, of the appearance in creation of air-breathing animals. Certain fossil beetles were found in

the coal-field of Coalbrook Dale; "a scorpion-like creature," a moth, and a land-crab were also presumed to be discovered. But our own time was to furnish new and most interesting additions. In 1844, Dr. King, of America, published an account of certain marks which he had found in the lower surface of slabs of sandstone, which slabs rested on thin layers of a fine unctuous clay. With equal discrimination and courage, he soon saw and announced to the world that they were the footsteps of a reptile that had walked over what was then the sands of some sea-shore. The doctor traced no less than twenty-three of these footsteps in the same quarry; and he considered that they were all left by one animal. Everywhere the marks showed a double row of tracks, the fall, in fact, at regular intervals, of a pair of feet. That this was an air-breathing, land-walking animal is considered to be proved by the depth of the impressions; under water, its weight would have been insufficient to have left such tokens of its presence. The cracks in the sandstone also show that the material had been exposed to the air and sun, and so had dried and shrunk. But as if to make quite clear and certain a fact so interesting in geological science, there was discovered the same year the skeleton of a reptile in the Coal measures of Rhenish Bavaria. This animal is supposed to have been related to the salamanders. In 1847 three other skeletons of animals, presumed to be allied to the crocodiles and lizards, were dug up at the village of Lebach, between Strasburg and Treves. The largest of these must have been three and a half feet long: its teeth seemed to have been of an advanced character in animal development. The smallest of the three is here represented half the natural size. The ARCHEGOSAURUS MINOR. creature had evidently weak limbs, such as could serve only to swim and creep. Lastly, in 1849, the footsteps of a large reptile were discovered in the lowest beds of the coal formation at Pittsville, near Philadelphia. This, then, is certainly the oldest inhabitant of the reptile class yet known in geological history. And so far as present facts go, we may presume that this was the period of the first appearance of air-breathing terrestrial animals on the globe.

Coal-beds do not entirely cease with the era.-Although coal-beds are not unknown in connection with a later era, such facts are but special exceptions to the general rule, which confines their production to the carboniferous period. Over the greater part of the earth's crust, the conditions that were so favourable for the production of a luxuriant vegetation ceased with the termination of the era; and where we do find later coal-beds, we may conclude that those favourable conditions had there existed proportionally longer.

Proportions of actual Coal veins to the Coal Strata.-The depths of the coal, as compared with those of the other strata in which they are imbedded, are very small. In the north of England, for example, the entire series of strata are estimated to extend to about three thousand feet, while, if we reckon all together the respective thickness of each of the twenty or thirty coal seams they inclose, they will not exceed sixty feet. In South Wales the Coal measures are of far greater depth, reaching the extraordinary thick

ness of twelve thousand feet, the result, says Sir Charles Lyell, "of fifty or even a hundred ancient forests buried one above another, with the roots of trees still in their original position, and with some of the trunks still remaining erect." We have more than once spoken of the awful ideas of time which geology gives us. Will any of our readers try to calculate for themselves, however roughly, on the preceding data, how long it must have taken to form the South Wales Coal measures-and then to estimate, if their fortitude will extend so far, the duration of the period that shall include the whole of the geological systems? They will then see that Geology is to time what Astronomy is to space. Both indicate the unfathomable. Both carry man to the extremest verge of his intellectual powers, and enable him, as it were, to look over trembling into the fearful abyss beyond. Both carry him at last in profound humility to God, whose help we require to enable us to stand fast amid such sublime phenomena.

Disturbances at the close of the period of the Coal Measures.-The period of the Coal measures evidently, then, closed in some abrupt manner. What were the causes ? Doubtless volcanic action. Everywhere through the system we see the tokens of the presence of mighty disturbing powers. For instance, the normal position of the coal-beds appears to be that of hollow basins, following the curve of the bottoms of the seas in which their materials were deposited. Everywhere these basins are broken up into pieces, some of which have been cast up on edge, while others have been greatly depressed. There is a famous slip of this kind in the Newcastle coal-field, known as the "Ninety-fathom Hitch," where one part of the same original basin lies no less than 450 feet lower than the other part. But such hitches are known to extend to a thousand or twelve hundred feet. We shall see that all this is owing to volcanic action when we examine what are

The Igneous Rocks associated with the Coal Measures.-These comprise greenstones (popularly known also as whinstones), clinkstones, basalts, and trap-tuffs. All these belong to what is called, geologically, Trap. The trap rocks of this era are distinguishable from those of other eras by their darker colours, greater proportion of bitumen in their composition, and by the prevalence of basalts and trap-tuffs, containing limestone, sandstone, and shale in fragments. Their positions may be described either as arising from a movement originally of a disruptive elevating character, as exhibited in the hills of the Mountain limestone, and the rounded heights and irregular cones of the Coal measures; or as overlying, where basalt and greenstone occur, looking as though primarily poured forth in a liquid state; or where trap-tuffs are found strewed about with all the appearances of having been vomited forth by volcanoes in the form of ashes, dust, or cinders; or, lastly, as interstratified, a position frequently occupied by the trap rocks, and which implies that they were of volcanic origin, and had been gradually covered by sedimentary deposits.

The Trap Rocks of the Coal Measures.-Can these varying kinds of rock have all issued from the same volcanic masses of heated and fluid matter? Experiment gives the following answer :-All the trap rocks may be fused into one homogeneous mass, and then made to assume the varying forms we have already described by mere differences accompanying the process of cooling. Let us illustrate these facts by the formation of basalt, the most interesting of all the trap rocks. Put a number of round pellets of plastic clay or putty into a vessel; then gently press upon them, and they will take

The

the shape of five or six-sided columns, precisely like those of basalt in the wonderful natural structures of Staffa and the Giant's Causeway. greatest known mass of basalt is that of the Deccan, in the East Indies, where it constitutes the surface of the earth for many thousand square miles. The traveller there often sees in the distance rising before him masses of broken columns, which induce him to believe he is approaching some important human structures, ruinous or otherwise. By the seaside such deceptive appearances are even still more common, especially where the columns are jointed, so as to seem built of separate stones. The dimensions

of these columns are sometimes most extraordinary. Some have been measured at Fairhead (the Giant's Causeway), which were found to be above a hundred yards high, while each of the sides was five feet_broad. Was not the idea of the clustered columns or piers of our cathedrals originally derived from this source?

Distribution, &c., of Coal.-Coal is largely distributed over the world. Independently of its abundance in our own country, it is found in France, Spain, Germany, Sweden, Russia, Hindostan, Australia, New Zealand, China, the Persian Gulf, Melville Island, Nova Scotia, Cape Breton, the United States, Chili, &c., &c. While thus adding to the wealth of many localities, it by no means conduces to their beauty; for

The Scenery of Coal Districts is universally tame, level, bleak, and unfertile, as though Nature had been aware that, in extracting the treasures from below, we should only have deformed and abused her gifts of whatever might have been most beautiful in scenery above, by the many useful, but far from ornamental contrivances and arrangements for the exhumation and transmission of coal that are found at all times around coal mines.

The Uses of Coal, &c., need scarcely to be spoken of, they are so well known and appreciated. Our position as a nation speaks trumpet-tongued as to what we owe to coal. With it we fuse our metals, produce steam,

light our streets and shops, &c., with gas, warm our houses, and prepare our food. The annual consumption in these islands alone amounts, we believe, to about thirty millions of tons annually; and as though that drain were not sufficient, we export some three millions more. How long will our coal mines stand this enormous demand? They are far from inexhaustible. Many persons of scientific attainments have looked at this matter with some interest, not to say anxiety. The conclusion they come to is, that a supply may be depended upon, possibly, for two thousand years-a long period in the history of human civilization, as we understand it, yet but a mere span, when looked at from the geological point of sight. But we may be quite certain that science, every day growing more fertile of practical benefits to man, will, long before the expiration of that time, have found much superior modes of obtaining all that coal can give us. Even now we hear almost daily of new discoveries in heating, lighting, and motive power, that happily promise to supersede the three great branches of usefulness that make coal so precious to us at present.

We may add, in concluding this chapter, that among the many felicities of natural arrangement, perhaps we can nowhere find one more striking than that which the Coal measures present of the abundance, all nearly together, of the three articles, coal, lime, and ironstone, which are so indispensable to the production of the metal iron in a form fitted for the fabrication of tools, machines, and structures of all kinds.

CHAPTER IX.

SECONDARY STRATA: THE NEW RED SANDSTONE AND THE OOLITIC SYSTEMS.

Deposition of the New Red Sandstone.-Upon and around the ruins, so to speak, of the carboniferous system, when broken up by violent volcanic action, were gradually deposited, by the renewed activities of nature, the strata known under the above designation. These include Red Sandstone, Variegated Shales, of yellow, purplish, and green colours (the green arising from the presence of oxide of copper), and Magnesian limestones, of a creamy colour, existing in thick beds, and frequently presenting interesting forms of structure, resembling now honeycombs, now bunches of grapes, &c.

The Colour of the Red Sandstone involves some interesting points of study. The grains of which it is in a great measure composed are not red, but consist of white, rolled, quartz sand, surrounded "like varnish" with the red peroxide of iron. From whence could the immense quantities of iron be obtained that were sufficient to colour the sedimentary deposits in question to the depth, perhaps, of a thousand yards, and over large portions of the world? Some writers say it could not possibly have been derived from the disintegration of the older rocks (though this is denied by Sir C. Lyell, who says the hornblende or mica contains the oxide of iron in sufficient abundance), and that, therefore, we must look to volcanic action as the true agency, which, to this day, is constantly ejecting the mineral referred to.