

LES REVOLUTIONS DU GLOBE 9 



from the living forms. It is only in the most recent 

 alluvions that we at length find species of animals 

 quite similar to our own. 



If, on the other hand, we descend lower into earth's 

 strata, we no longer find mammals, but only ovi- 

 parous quadrupeds. The chalk contains numerous 

 tortoises, crocodiles, and, at the Mont Saint Pierre 

 in Maestricht, a gigantic marine lizard, the Moso- 

 saurus. In the ferruginous sands below the Chalk 

 we observe in England, besides the crocodiles 

 and the tortoises, some large reptiles, some car- 

 nivorous like the Megalosaurus, others herbivorous 

 like MantelPs Iguanodon. Still lower down, the 

 compact limestone of the crests of the Jura con- 

 tains, near Soleure, a considerable number of species 

 of fresh-water tortoises, or Emydes. In the Jurassic 

 schist and limestone is found a world of reptiles, of 

 various forms and sometimes of gigantic size the 

 Ichthyosauri, the Plesiosauri, gavial-like Crocodiles, 

 the remarkable Megalosaurus, and the flying lizards 

 or Pterodactyls. Still further back, reptiles are again 

 found in the conchiferous limestone of the Muschel- 

 kalk of Germany and Lorraine. Finally, it is in 

 the cuprous and bituminous schists of Thuringia 

 that we observe the first trace of oviparous quadru- 

 peds, in the form of reptiles similar to our great 

 Monitors, accompanied by fish of an unknown genus. 



Thus Cuvier not only showed the presence in the 

 sedimentary strata of a series of terrestrial faunas, 

 superposed and distinct, but he was the first to 

 have, and that very clearly, the notion of the 

 gradual organic improvement in these faunas, from 

 the earliest to the most modern. This is a funda- 



