274 COSMOS. 



Thuringia ; the Palasosaurus and Thecodontosaurus of Bris- 

 tol are, according to Murchison, of the same age. The Sau- 

 rians are found in large numbers in the muschelkalk,* in the 

 keuper, and in the oolitic formations, where they are the most 

 numerous. At the period of these formations there existed 

 Plesiosauri, having long, swan-like necks consisting of thirty 

 vertebrae ; Megalosauri, monsters resembling the crocodile, 

 forty-five feet in length, and having feet whose bones were 

 like those of terrestrial mammalia, eight species of large-eyed 

 Ichthyosauri, the Geosaurus or Lacerta gigantea of Som- 

 mering, and, finally, seven remarkable species of Pterodac- 

 tyles,t or Saurians furnished with membranous wings. In 

 the chalk the number of the crocodilial Saurians diminishes, 

 although this epoch is characterized by the so-called crocodile 

 of Maestricht (the JVIososaurus of Couybeare), and the colos- 

 sal, probably graminivorous Iguanodon. Cuvier has found 

 animals belonging to the existing families of the crocodile in 

 the tertiary formation, and Scheuchzer's antediluvian man 

 {liomo diluvii testis), a large salamander allied to the Ax- 

 olotl, which I brought with me from the large Mexican lakes, 

 belongs to the most recent fresh-water formations of CEnin- 



^^"•i . . . . ■ 



The determination of the relative ages of organisms by the 



superposition of the strata has led to important results regard- 

 ing the relations which have been discovered between extinct 

 families and species (the latter being but few in number) and 

 those which" still exist. Ancient and modern observations 

 concur in showing that the fossil floras and faunas differ more 

 from the present vegetable and animal forms in proportion as 

 they belong to lower, that is, more ancient sedimentary for- 

 mations. The numerical relations first deduced by Cuvier 



Saurian asserted to have been found in the mountain limestone (car- 

 bonate of lime) of Northumberland (Herm. von Meyer, Palceologica, s. 

 299), is regarded by Lyell {Geology, 1832, vol. i., p. 148) as very doubt- 

 ful. The discoverer himself referred it to the alluvial strata which 

 cover the mountain limestone. 



* F. von Alberti, Monographie des Bunten Sandsteins, Musclielkalk» 

 und Keupers, 1834, s. 119 und 314. 



t See Hermann von Meyer's ingenious considerations regarding the 

 organization of the flying Saurians, in his Palceologica, s. 228-252. In 

 the fossil specimen of the Pterodactylus crassirostris, which, as well as 

 the longer known P. longii'ostris (Ornithocephalus of Sommering), was 

 found at Solenhofen, ir the lithographic slate of the u[)per Jura forma- 

 tion, Professor Goldfass has even discovered traces of the membranous 

 wing, "with the impressions of cui'ling tufts of hair, in some places a 

 full inch in length." t [Ansted's Ancient World, p. .56.] — 7V. 



