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here shown were supposed to be mere portions of the extremity of the arms of a huge dome-shaped body, which divided into twelve limbs, each extending horizontally from the edge of the dome. For a long time this

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vegetable wonder baffled all conjectures as to its particular relationship with other plants, but at last it was discovered to be the root of the plant next mentioned the Sigillaria-of which we likewise present a fine specimen above.

A large portion of the trees of the era belonged to this tribe, which grew to the height of seventy feet, with regular cylindrical stems, and without branches. The ornamental-looking studs show the places where the leaves were inserted. To the colliers of Newcastle and other places these fossil stems are but too familiar, under the name of coal-pipes, for they are a continual source of accidents. In mining they are often left in a vertical position in the masses of coal that extend overhead, and as they are very heavy, have no branches to support them, are broader at the base than above, and are merely supported by the cohesion of a thin layer of coal, which has replaced the bark, and is connected with the surrounding mass of coal, no sooner does this coating give way, than the column drops out of its bed, sometimes obliquely, sometimes perpendicularly, and kills or injures the workmen below.

There is one plant also very common in the Coal measures, which, were it only for its gracefulness, must be mentioned-the

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It was probably allied to the Sigillaria. It is found in the Newcastle Coal measures. We need only to add to the foregoing enumeration the pines, which seem to be allied to the Araucarias, that have of late been so much spoken of in the gardening world, as among the most magnificent of existing coniferæ. As an interesting evidence of the resources of science, we may mention how the discovery was made of the nature of these trees. A gigantic tree trunk was found at Newcastle; there were no flowers or leaves: how were botanists to determine what tree it was? Some ingenious naturalists soon answered this query. They cut off very thin cross slices of the stem, polished them to the highest possible degree, and then submitted the slices to the microscope, when, lo! there were at once visible the peculiar "reticulations" which distinguish the cone-bearing trees, and the particular tree was soon decided to be an Araucaria.

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No Grasses, Herbs, Shrubs, &c., in the Coal Measures. In reviewing these names we perceive there are no grasses, no herbs, no shrubs, although all these now abound wherever vegetation flourishes. How is this? Are we to assume that they were all absent from the Flora of a time that was infinitely more rife than our own with the influences that develope vegetable life? The Coal measures, as we have seen, afford about eight hundred species; but our present vegetation contains at least eighty thousand! Do these numbers correctly illustrate the comparative meagreness of the one period, and the wealth of the other, as regards variety of life? has been given by one of our most distinguished botanists, Dr. Lindley, who tried the following experiment:-He threw one hundred and seventy-seven plants into a vessel of fresh water. Among them were species that belong to the same great natural orders as those of the Coal measures, and others belonging to those orders most commonly diffused over the earth at the present day. His object was to learn whether the last would perish sooner than the first, and so afford an explanation of their absence from the Coal strata. In two years one hundred and twenty-one species had disappeared, and of the fifty-six that remained, the most perfect specimens were those of coniferous plants, palms, club-mosses, and ferns with their organs of fructification destroyed-in short, the very same generic kinds of plants that have been so long preserved in the Coal measures; and with regard to the ferns, in precisely the same state of partial and peculiar injury.

Had England, &c., at the time a Tropical Climate?--The tropical character of much of this vegetation is a startling phenomenon. Was there a tropical climate in England when the plants flourished that now form its coal beds? Was there a tropical climate in Newfoundland, which is now still colder than England? or in Melville Island, whose naked hyperborean plains make one shiver only to think of? All these places have their coal beds, and in all there must have once grown a rich and stately vegetation. In Melville Island the difficulty is enhanced by the geographical peculiarities of the sun's influence. For ninety-four days this luminary is never above the horizon, and for yet another hundred and four days he never sets. Puzzled by these difficulties, some have even asked the question-"Has the earth changed the position of its axis ?" to which, we think, an answer may be given very decidedly in the negative. Dr. Lindley's explanation is, that we are probably deceived in the apparent analogy that exists between plants now living, and that grow only in tropical countries, and the plants of the Coal measures, and that the latter were not, therefore, after all, tropical; and where an analogy does exist; he shows that plants, belonging generally to a

tropical clime, may yet have members of the family capable of enduring our severest winters. And he gives various instances in point. But all this while it seems to be forgotten that the ground temperature must have been very high all over the world, if the theory already developed, with regard to the earth's gradually cooling down from a state of intense heat, be true. And if such a ground temperature existed, of course there must have been a climate in some respects analogous to the hotter ones of our own eraprobably, indeed, much more fervid than any one we now have experience of. The extreme abundance and gigantic size of the coral flora have been also attributed to the existence in the air of an extraordinary quantity of carbonic acid, the gas from which is derived the carbonaceous substance of all plants. M. Adolphe Brongniart, the author of this speculation, points, in corroboration of its truth, to the fact that there is hardly a trace of the existence of any land animals at the time this magnificent vegetation was in existence-the very excess of carbonic acid that nourished the one poisoning the air for the latter. It is by no means clear, or even probable, that the proportions of the atmospheric elements are always the same. Now, if the whole of the coal beds in Great Britain alone were again to be reconverted into carbonic acid, the effect would be to increase the proportion of the former to the latter from a thousandth part, as at present, to the eight hundred and fiftieth part. We may add, in conclusion, that the most eminent botanists, from Jussieu downward, have generally considered the coal plants to indicate the existence of a warm climate in their locality at the time they were growing. To sum up, therefore: the high ground temperature, and the excessive quantity of carbonic acid in the atmosphere, with possibly some minor but still important differences in the capacity of the latter, then and now, for the transmission of light and heat, seem, therefore, to furnish the true explanation of our finding such plants as tree-ferns in the coal of England, of Melville Island, and of Baffin's Bay-plants that now exist only in the very deepest recesses of the primeval forests of the torrid zone, breathing a damp and unchanging atmosphere, and living alone-true vegetable hermits, without even a neighbour or a parasite to while away the sultry hours. We must give our readers the pleasure of looking upon one of these extremely picturesque and oriental-looking plants in a better state than any fossil will admit. The following engraving repre

sents a

LIVING TREE-FERN.

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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 stráta 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

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