Fossil Ferns. As far as has been yet determined from the rocky tablets of the earth's crust, ferns first appeared in the Devonian period, and these comprised both herbaceous and arborescent species.
In the immediately succeeding Coal-period they appear to have reached their maximum development. The dense forests and the moist atmosphere of this period were so suited to their growth that they formed a large bulk of the vegetation. Several hundred species have been described, some of them tree-ferns of a size fitting them to be the companions of the immense Sigillarias and Lepidodendrons whose remains are found associated with theirs in the Carboniferous rocks. In the Permian rocks comparatively few ferns have been met with, but these rocks are as a whole not rich in organic remains. Numerous new forms appear in the Trias, and their number is increased in the Jurassic. The Cretaceous strata being chiefly of marine origin, land-plants are not abundantly met with. But the evidence supplied by the Wealden beds of England and strata on the same geological horizon in Germany shows that ferns were at that time prominent forms in the vegetable life of the globe. In the Tertiary strata ferns are rather rare.
FOSSIL FORESTS have been frequently observed in the Coal-measures. The seams of coal having in general been formed from the vegetation of the locality where they occur, it is to be expected that when the coal is removed the stools and roots of the trees will be observed in the immediately subadjacent bed of clay or shale—the ancient soil. Such a forest was laid bare in an open work at Parkfield Colliery, near Wolverhampton, in 1844. In the space of about one-fourth of an acre the stumps of 73 trees, with their roots attached, appeared as shown in the annexed ground-plan. The trunks, broken off close to the root, were lying prostrate in every direction, often crossing each other. One of them measured 15, another 30 feet in length, but they were generally shorter. They were invariably converted into coal, and flattened to the thickness of 1 or 2 inches. The upright stems show that some of them had a circumference of more than 8 feet. A fossil forest was uncovered near Glasgow in 1887. Similar fossil forests have been observed in the coalfields of Nova Scotia, and have been carefully described by Lyell, Logan, and Dawson. The usual height of the trees observed by Lyell was from 6 to 8 feet; but one tree was about 25 feet high, and 4 feet in diameter. Brongniart describes the remains of a fossil forest preserved in an upright position, in strata of micaceous sandstone, belonging to the Coal-measures at St Etienne, near Lyons. Though most abundant in strata of the Carboniferous period, fossil forests have been observed in other formations. The Dirt-bed (q.v.) of the Lower Purbeck series is the remains of an ancient forest. Instances are also abundant in strata of later age.
The remains of ancient forests belonging to a geologically recent period are to be found in and underneath beds of peat. There is good evidence that some kinds of peat had their origin in the destruction of forests. Trunks and branches of oak, hazel, fir, &c. are found in them, and the roots of the trees may be traced in the underclay. Round the coasts of the British Islands and the opposite shores of the Continent remains of ancient forests are frequently to be seen at low-water, the stools of the trees evidently occupying the place of growth. The occurrence of these so-called 'submerged forests' shows that within recent times there has been a loss of land in north-western Europe. See GEOLOGY, PALEONTOLOGY, PLEISTOCENE SYSTEM, &c. The discussion of fossil footprints, the tracks of animals or other moving things, on mud or sand now indurated into rock, is sometimes called Ichmology.