or within the mountain valleys of equinoctial regions.

From this circumstance we learn, that a high temperature must have prevailed in those days even in the polar regions of the earth, inasmuch as the Coal strata are found in great abundance, not only in the temperate, but in the frigid zones -in India and Australia, in the southern hemisphere; and in Melville Island and Baffin's Bay, in the northern. Such a temperature could not have been caused by the influence of the sun in latitudes so remote from each other, and must, therefore, have proceeded from the earth itself. Here again, we have evidence of the existence of the internal or central heat of the globe, and of the continuance down to this period of its history. The true explanation is, that the incandescent globe had not sufficiently cooled to admit of animal or vegetable life in the Azoic or Cambrian era, but was sufficiently cooled, during the Silurian and Devonian epochs, to permit of the creation and existence of Zoophytes, Mollusks, Crustaceans, Fucoids, and certain classes of fishes

2 Coal is not confined to the Carboniferous system. Anthracite coal, the product of marine plants, is found in the Silurian strata in Ireland and Portugal. In Spain, mines of the same mineral are worked in the Devonian; and in Saxony, in the Permian system. The Oolites of Scotland, America, and the East Indies, also yield coal; and the brown coal of Germany and Austria is found in the Meiocene of the Tertiaries. But in none of these places does the mineral approach in quality or extent the product of the great coal measures of the Carboniferous system.

F

and plants; and had become genial enough, during the Carboniferous era, to foster the rich luxuriant vegetation that formed its distinguishing characteristic. The extensive exhalations of carbonic acid gas which issued from the tepid earth, mingling with the atmosphere, must have assisted this profuse growth. According to Humboldt, “it is very probable that in an earlier condition of the globe, far greater emissions of carbonic acid gas mingled with the atmosphere, and heightened the process by which plants assimilate carbon; and thus vast forests were formed, which in subsequent revolutions were destroyed, and inexhaustible stores of fuel (lignites and coal) were buried in the terrestrial strata thus forming at the surface." "

But not only have geologists ascertained the general vegetable structure of the Coal measures, their researches have disclosed the nature and character of the several plants, which enter into the composition of the mineral; and which, therefore, must have clothed the earth at the period of their formation. A brief consideration of the various species of the trees of this primeval era, and of the climatal conditions of the earth and atmosphere necessary for their production, will prove, not merely interesting and instructive as a scientific inquiry, but of great value in its consequences to the cause of the truth and inspiration of the Scripture record of the creation.

The plants which have contributed most exten

3 Cosmos, vol. i. p. 190.

sively to the formation of Coal, are referrible to five different genera, viz. Ferns, Calamites, Lepidodendra, Sigillaria, and Stigmaria. They are thus enumerated by Dr. Buckland, and all succeeding geological writers.

FERNS. Of this tribe of plants there is a singular preponderance among the Coal fossils, insomuch that it has been termed the master form or type of the Carboniferous era. In the great Coal formation there are, according to Brongniart, about 250 ascertained species of Ferns, forming about one half of the entire known Flora of this formation; and Mr. Brown, in the Appendix to Tuckey's Congo Expedition, states that the circumstances most favourable to the growth of Ferns are Humidity, Shade, and Heat-a fact well known to all botanists.

4

diameter of the Equisetum of the present day rarely exceeds half an inch, the Calamite of the 4 Bridgewater Treatise, vol. i. p. 464.

Carboniferous age frequently exceeds a foot in diameter, and is many yards in height. The stems, when found in horizontal, or nearly horizontal positions, are compressed and flat, indicating that the plant was soft and succulent in its

tribution; and were, therefore, produced under similar climatal circumstances of shade, heat, and moisture. They attained an enormous size in the Carboniferous era, the fragments of the stems occurring from twenty to forty-five feet in length, and upwards of four feet in diameter. They are also found compressed and flattened in the coal mines, attesting the softness and succulency of their structure.

SIGILLARIA are a species of plants unknown to modern vegetation, though very abundant in the

Coal formation. They are described by Dr. Buckland as lying inclined at all degrees throughout the coal strata; "but are most frequently prostrate, and parallel to the lines of stratification, and in this position are usually compressed." When erect, or highly inclined, the interior is filled with sand or clay; from which he infers, that "the bark, which alone remains, and has been converted into coal, probably surrounded an axis composed of soft and perishable pulpy matter," which by decay made room for the sand and clay. They attained the extraordinary dimensions of from fifty to seventy feet in height, and from half a foot to three feet in diameter. Brongniart enumerates forty-two species of Sigillaria, and considers them to have been nearly allied to arborescent Ferns.

STIGMARIA, from the length and form of their

shaped trunk or stem, three or four feet in diameter, the substance of which was probably yielding and fleshy." It has, however, been discovered,