452 THE POPULAR SCIENCE MONTHLY, 



his perpendicular rays much farther from the equator than now, the 

 torrid zone would be thus enlarged. The calmer light, the more gen- 

 tle and equalized heat, the thicker and more humid atmosphere, explain 

 that equalization of temperature, those days half veiled and transpar- 

 ent 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 out- 

 set 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. Sa- 

 porta takes care to warn us against this error. " Nature, always ac- 

 tive," says he, " has had no intermittence nor time of sleep. Life, 

 since its first appearance, has not ceased to inhabit the earth. De- 

 pressed 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 peri- 

 ods : 1. The Primordial or eophytic, corresponding to the Laurentian, 

 Cambrian, and Silurian ; 2. The Carboniferous or paleophytic, compre- 

 hending 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 neop>hytiCy em- 

 bracing all the formations from the chalk of Rouen up to and includ- 

 ing the Pliocene. 



The flora of the eophytic period is unknown. The debris 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 



