THE REVOLUTIONS OF THE CKUST OF THE EARTH. 319 



epochs and formations quite as well as the Brachiopods, or, among the 

 plants, Equisetacea. The first series is composed of Orthoceratites, of 

 Belemnites, and of Sepias; until the Zechstein, the Orthoceratites predom- 

 inate, and after along period appear in great numbers the Bclcmnites, 

 which disappear in the Chalk, leaving no representatives, unless in the 

 cuttlefish and the sepia of our sea, of which fossil species are also 

 found. The Ammonites form the second series, which commence with the 

 Graywacke, and continue to the upper strata of the Chalk. The cham- 

 bered Cephalopods are remarkable for the rapidity with which they 

 developed into genera and species, aud still more so for their quick dis- 

 appearance after a renewal of the same forms in the Bacidites, Scaphites, 

 Turrilites, Hamitcs. It is a question whether with the sudden disappear- 

 ance of the Crinoids, of the Belemnitcs, and a larger part of the Sauri- 

 ans, the conditions of animal life were not completely changed after the 

 Jurassic period. The abrupt extinction of certain organisms is repeated 

 quite often in the lqstory of the sedimentary crust, aud at intervals so 

 regular that to attribute it to a fixed law, independent of all biological 

 processes, is in accordance with all the facts furnished by contemporary 

 geology, concerning the changes which have modified the surface of the 

 globe. These fossil remains are a powerful auxiliary for the demonstra- 

 tion of this law. 



The Crustaceans appear with the Trilobites, animals of a peculiar struct- 

 ure, which have no analogues among the Crustaceans now living. Their 

 eyes, of complicated structure, are, according to Buckland,* the most 

 ancient testimony of the existence of light. Other Crustaceans after- 

 ward appear, but have more analogy with those of the present time. 



Insects are found iu great numbers, distributed among the fossil plants 

 of the Coal formation ; later they are found in the Lignite or in yellow 

 amber, which is the fossil gum of the Pinnites succinifer. 



The large class of Fishes commence with the mica-schist. Professor 

 Agassiz f divides the largest number of the fossil species into four orders, 

 two of which, the Ganoids and the Placoids, continue from the mica- 

 schist until our day, while the Ctenoids and the Cycloids are observed 

 only since the Chalk. The fish of the primitive world were organized 

 in accordance with the nature of the medium they inhabited. The most 

 ancient were enveloped in a veritable armor of scales, which protected 

 them from the violence of the elements. In course of time this envelope 

 grew thinner, and at last disappeared. 



The first traces of reptiles are found iu the Zechsteiu,in the Protosaunix, 

 which is not found in the following deposits. Some foot-prints found 

 in the Old Red Sandstone have been attributed to saurians. Iu the 

 Triassicformation we find the Dracosaarus, the Kotosaurus, the Phytosau- 

 rus; iu the Jurassic formation, the Ichthyosaurus, the Plesiosaurus, the 

 Teleosaums, and other species not less strange in form and proportion ; 



* Pouchet, L'Univers, note 94, p. 420. 



t Researches upon Fossil Fish, t. i., pp. 105, 172. 



