Page:Popular Science Monthly Volume 34.djvu/248

236 temperature has permitted them to maintain themselves sporadically.

By regarding these considerations and this presumed march, we succeed in determining the connection between recent and fossil species, and evidences of affiliation between them. There also exist relations not to be neglected between some recent types and other old ones which we can not believe to be wholly lost, and others between present forestal groupings taken separately and those which have succeeded one another through the ages; but the further we go back, the more we address ourselves to a distant order of things, the less tangible are these relations found to be. Of all the Carboniferous vegetation there remain only isolated or dwarfed types, as of Equisetæ, ferns, and club-mosses. The singular Japanese gingko, and perhaps the dammara of the Indian Archipelago, can trace their ancestry back to that period. A greater number of estrays have survived from the Secondary ages; but they are still rare—auracarias, cedars, pines, thuyas, and a few colonies of cycads south of the equator. There has been something vague and undetermined about the "foliage" trees since they first appeared in the Cretaceous period; but their evolution and characteristic physiognomy have been tending to fix themselves. The magnolia, tulip-tree, plane-tree, ivy, etc., have hardly varied since then; but the subsequent modifications of other European flora have been so frequent and profound that no collection of existing species corresponds except by partial traits that have been questioned with the Cretaceous vegetation. The correspondence is somewhat closer with the vegetation of the Eocene, especially of the later Eocene. The examination of certain floras which are referred to this horizon has shown that vegetation has not varied much since then, except from the impoverishment which it has suffered by the subsequent elimination of some types, and the addition of a number of deciduous types of later introduction. Thus, a considerable proportion of forms, the ancestors of which appeared in the Eocene, have persisted in place from that epoch, while those which have since migrated are found in more southerly regions.

It is in the Miocene, particularly in the later Miocene, that the relations become manifest of the deciduous trees of southern habit which we have spoken of as being dispersed over various points of the Mediterranean domain—the plane-tree, the liquidambar, the planera, the linden, the vine, some hornbeams and ashes, the datepalm, the pomegranate, etc.; and the lauriferous grouping of the Canary Islands, preserved intact by means of its insular situation and of the persistency of local climatological conditions, reproduces unchanged the picture of a mountain-forest of central Europe, as recent discoveries have shown it to have been in the