54 LIAS, OR LIASSIC SYSTEM. 



FIFTH GEOLOGICAL EPOCH. 



Lias, or Lia'ssic System Jura'ssic Formation O'olitic System. 

 (Secondary formation Continued.) 



33. Up to th'is period of its geological history, we have seen the 

 earth was inhabited only by plants, some inferior animals, such as 

 zo'ophytes, mollusks and fishes, and lastly, by some reptiles. Dur- 

 ing the period at which we have now arrived, this state of things 

 changed, and there was created a new fauna composed of most 

 remarkable animals, characterized especially by a multitude of 

 reptiles, of strange form and gigantic size. 



34. The formation of the LIAS so called from a barbarous pro- 

 vincial word, supposed to be a corruption of layers, and to allude 

 to the riband-like appearance of the rock when seen in section 

 the Lias consists of strata, in which an argilla'ceous character pre- 

 dominates throughout, but which are also remarkable for a quan- 

 tity of calcareous matter mingled with the clay, and forming 

 occasional bands of argilla'ceous limestone. A few beds of sand- 

 stone also alternate with the clay and marl, and are sometimes 

 mixed with the latter, forming a marly sandstone of a white or 

 greenish colour. 



35. The inferior layers of the lia'ssic system are characterized, 

 according to M. Leymerie, by the presence of the Pecten lugdu- 

 ne'nsis (Jig. 69), and different species of echi'nidx of the division 

 diade'ma (Jig. 70). 



Fig. 69. Pt'cten Ivgdune'nsis. Fig. 70. Diade'ma seria'le. 



36. The middle layers, or the lias proper, are distinguished 

 especially oy the presence of the Gry'phea arcua'fa, (jig> 71), and 

 the ammonite named after Dr. Buckland, (Jig. 72), the spi'rifer of 



33. What is remarked of the animals in the early geological periods ? 



34. Of what is the Lias formation constituted ? 



35. What animal remains characterize the inferior beds of the Lias 7 

 36 How is the Lias proper characterized ? 



