Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/346

 342 takes place of the simpler forms which predominated through the two preceding periods., Smaller Equisetaceæ also succeed to the gigantic Calamites; Ferns are reduced in size and number to the scanty proportions they bear on the southern verge of our temperate climates; the presence of Palms attests the absence of any severe degree of cold, and the general character marks a Climate nearly approaching to that of the Mediterranean.

We owe to the labours of Schlotheim, Sternberg and Ad. Brongniart the foundation of such a systematic arrangement of fossil plants, as enables us to enter, by means of the analogies of recent plants, into the difficult question of the Ancient Vegetation of the Earth, during those periods when the strata were under the process of formation.

Few persons are aware of the nature of the evidence, upon which we have at length arrived at a certain and satisfactory conclusion, respecting the long disputed question as to the vegetable origin of Coal. It is not infrequent to find among the cinders beneath our grates, traces of fossil plants, whose cavities having been filled with silt, at the time of their deposition in the vegetable mass, that gave origin to the Coal, have left the impression of their forms upon clay and sand enclosed within them, sharp as those received by a cast from the interior of a mould.

A still more decisive proof of the vegetable origin, even of the most perfect bituminous Coal has recently been discovered by Mr. Hutton; he has ascertained that if any of the three varieties of Coal found near Newcastle be cut into very thin slices and submitted to the microscope, more or less of vegetable structure can be recognised.

i. e. increase externally by the addition of concentric layers from without; these form the rings, which mark the amount of annual growth in the Oak and other forest trees in our climate.