GEOLOGY. 



689 



footsteps. On the same beds have been observed the 

 prints of three-toed feet, considered by some geologists as 

 traces of the first birds on onr globe. 



To this period belong the Jnrassic strata, which play so 



278. Labyrintliodon restored. 



important a part in the formation of the Jura Mountains, 

 from whence they derive their name. This formation is 

 rich in animal fossils, which give it quite a special cha- 

 racter. It may be divided into two sections — the Lias 

 and the Oolite. 



The liassic seas fed numbers of animals, and their 

 deposits are distinctly characterized by the gryplia?as, 

 ammonites, l)elemnites, plagiostomata, and encriuites, 

 which are peculiar to it. But Avhat impresses a special 

 stamp upon it is the presence of strange marine reptiles, 

 the remains of which are found in it remarkably well 

 preserved. 



