Page:Popular Science Monthly Volume 16.djvu/478

452 his perpendicular rays much farther from the equator than now, the torrid zone would be thus enlarged. The calmer light, the more gentle and equalized heat, the thicker and more humid atmosphere, explain that equalization of temperature, those days half veiled and transparent nights, and that tepid climate of the polar regions, that we might consider as presiding at the development of primitive life. Finally, the primitive sun, by its slow condensation, passing insensibly into its present state, necessarily forced the retreat of the torrid zone, thus ending the anterior equality of the climate, permitting cold to become established at the pole, and concentrating heat at the equator. Such is the bold but attractive hypothesis of M. Blaudet. No doubt it leaves many points obscure, but the numerous partisans of the theory of Laplace will not hesitate to acknowledge its importance, for, in reality, it is part of the theory itself.

It remains now to review the remarkable chapter that Saporta has given to the study of vegetable periods. We may remark at the outset that this word "period" implies no such general convulsions as the first geologists believed in, who supposed the history of the globe broken into sharp periods, each of which was inaugurated by a distinct creation and terminated by a sudden and universal destruction. Saporta takes care to warn us against this error. "Nature, always active," says he, "has had no intermittence nor time of sleep. Life, since its first appearance, has not ceased to inhabit the earth. Depressed sometimes, interrupted never, there has circulated without respite a constantly fertile sap. The epochs and revolutions which geologists have named are valuable only as serving to introduce great dividing lines in the bosom of an incalculable duration, but a closer view reveals these beings always succeeding each other; the extinction of some among them would not prevent survivors from occupying their place. Physical revolutions, essentially accidental and unequal, have never been radically destructive. If some periods have been less favorable than others to the development of life, these relatively impoverished intervals have possessed organized beings that, afterward multiplying and diversifying, have easily repeopled the globe."

Saporta divides the world of fossil vegetables into four great periods: 1. The Primordial or eophytic, corresponding to the Laurentian, Cambrian, and Silurian; 2. The Carboniferous or palæophytic, comprehending the Devonian, Carboniferous, and Permian; 3. The Secondary period or mesophytic, commencing with the Trias and reaching to the end of the chloritic chalk; 4. Finally, the Tertiary or neopyhytic, embracing all the formations from the chalk of Rouen up to and including the Pliocene.

The flora of the eophytic period is unknown. The débris which represents it has in general a character so vague that there is yet no agreement upon its true nature. The graphite found in the Laurentian indicates, however, that from this epoch vegetables existed in great