REVOLUTIONS OF THE EARTH. 



historic times, and the species of which are now totally extinct. 

 In general, they differ from species now living, more and more, in 

 proportion to the antiquity of the strata m which they are found, 

 and, in most of the strata of the earth's crust we find certain 

 species which are not met with either in more ancient or more 

 recent formations. 



4. It is hy comparing the fossils with each other, and by com- 

 bining this study with that of the order of superposition, in which 

 the different strata are found, and with their mode of formation, 

 that we have arrived at a knowledge of the earth at periods long 

 anterior to the creation of man, and are enabled to trace the his- 

 tory of the great revolutions which have successively disturbed 

 and changed its surface. 



5. We learn by this study that the physical condition of the 

 surface of the earth, as well as that of the organized beings by 

 which this surface is inhabited, has undergone great and nume- 

 rous changes. Entire creations of animals and of plants have sue 

 ceeded each other ; a'ter having peopled the waters and inhabited 

 the land for ages, each in its turn has been destroyed by some 

 great catastrophe of nature, and given place to a new creation. 

 But the appearance of a new flora, or a new fauna, the destruction 

 of living beings, and the deposit of enormous beds of rocks, are 

 not the only phenomena which characterize the great revolutions 

 of the earth. At different epochs, total overthrows, of which the 

 most fearful earthquakes and volcanic eruptions of our times can 

 give but a very feeble idea, have raised up the solid crust of the 

 globe, and produced lofty chains of mountains, whose elevation, 

 immense as it appears to us, was even still greater before the val- 

 leys and basins that separate them were gradually filled by new 

 deposits. 



6. The great revolutions of the earth appear to have been sepa- 

 rated by long periods of tranquillity, during which animals and 

 plants multiplied on different parts of the globe's surface, and de- 

 posits of solid materials, borne by the waters or drawn from the 

 bosom of the earth, were heaped up, constituting beds of rocks of 

 greater or less thickness, and varying in their nature, in the sub- 

 stance of which were entombed the remains of contemporaneous 

 animals and plants. 



7. The natural history of the globe is written in the very rocks 

 of which our planet is composed, and the study of these ancient 

 monuments of the power of the CREATOR teaches us what tran- 

 spired long before the existence of man on the earth. These fos- 



4. By what means do we study the geological history of the earth? 



5. What are the great facts taught by the study of geology ? 



6. What seems to have occurred in the long intervals of tranquillity 

 between the great geological revolutions of the earth? 



7. Does geology teach us that the earth was always inhabited by man ? 



