Page:Popular Science Monthly Volume 16.djvu/483

 sort witnessed the successive appearance of different classes of plants, we have seen the rising and falling movements of vegetation, periods of activity alternating with periods of relative repose, and that succession, or better, that procession of phenomena which has enabled us, if not to comprehend, at least to prove the transformations of life that all together are called evolution.

We shall find analogous phenomena in the series of Tertiary time, to which Saporta has given his longest chapter. This part of his work contains many descriptions of plants. They show us more than the simple succession of flora. The growing differentiation of the divers types and the consequent multiplication of species conduct us insensibly to the actual vegetable world. We see the growth of local flora, some of which are so clearly defined that we are able, by the aid of the imagination and of some well-preserved fragments, to reconstruct the principal genera and species of which they were composed. Fig. 1 represents a group of these plants so restored. The numerous modifications undergone by the vegetable kingdom during the Tertiary age, the formation of local floras, etc., are easily explained if we recall what was before said, of the influence of the medium upon living beings, and especially upon plants, that can not escape. Climatic equality no longer exists. The European Continent, up to this time made up of islands, tends now to aggregate and take on its present form; the soil

 (Types of entire leaves): 1. Quercus Lamberti (Wat.) (Paleocene). 2. Quercus tæniata (Sap.) (Middle Eocene). 3. Quercus macilenta (Sap.) (Middle Eocene). 4. Quercus paleophellos (Sap.) (Upper Eocene). 5. Quercus ellptica (Upper Eocene). 6. Quercus salicina (Upper Eocene).

is subject to movements of oscillation, which often change the configuration and relief of various countries. Lakes of fresh water are formed, and then disappear. The nature of the soil varies as marine deposits recapture it from deposits of fresh water; and reciprocally.