The number of known existing ferns amounts to between seven and eight hundred, of which about fifty species belong to Great Britain, and upward of two hundred to the inter-tropical island of Jamaica. Nearly two hundred fossil species have been discovered in the British coal strata alone. The fossil genera most common to the district around, and occurring in every section of the great valley of the Scottish lowlands, are cyclopteris, neuropteris, pecopteris, and sphenopteris. The shales and clay-ironstones in which these beautiful plants are detected, are generally of a dark brownish color, while the impressions are all of the deepest jet, bringing out in lively contrast the complete cast of the fronds. There is a great resemblance between the specimens of extinct ferns and the existing families of our filices, now growing on every hill, brae, or mountain corrie; and, if this were all the difference, nature would seem to have departed but little from her original models. But the presumption is that most, if not all, the ferns of the coal era were trees which attained to a great height, and similar to the tree-ferns now growing so abundantly in the islands of the Pacific. The decorticated stems and trunks are deeply indented with scars, the markings, it is supposed, of the fronds which dropped from their feathery sides. This inference is borne out by the additional circumstance, that the fossils are generally much flattened and compressed, as would necessarily happen to succulent plants and such trees as consisted of the cellular tissue of the endogenous class. What a striking change in the vegetation of our country, where purple heaths, and cheerful grasses, and luxuriant corns, and forests of every tint and structure, have replaced the long green stems, and dark somber hues of the fern-clad regions of the olden times! The remains of this tribe are so numerous as to have stinted, one would suppose, or utterly to have prevented the growth and increase of every other order of plants, bringing before the imagination the scenes of our Australian colonies, so wild and wondrous to European eyes—and carrying back the mind to the vision of primeval ages, through a long succession of times and their events, the vista of an infant world.