558 MANUAL OF NATUEAL HISTORY. 



Tubingen. The curious Russian fish Ommotolampes 

 Eichwaldi of Fischer, which is covered with bony 

 shields like a tortoise, and the no less remarkable 

 genus Trachelocanthus, which has a spine in its 

 throat turned backwards, belong to this period. 

 The other fish are remarkable for their heterocercal 

 tails, in which the vertebral column extends into the 

 upper lobe, as seen in the Shark and Sturgeon, which 

 the fossil Palceoniscus probably resembled in its 

 habits. The remains of molluscous animals are 

 referred principally to the brachiopodous genera, 

 Productus and Spirifer. 



III. CLASS.— SECONDARY-FORMATIONS. 



Secondary formations, as now restricted, are com- 

 posed of various strata of sandstones, aluminous and 

 siliceous beds, and chalky deposits ; they commence 

 with the New Red-Sandstone, and comprehend be- 

 sides the Lias, the Oolitic series, including the 

 Wealden-group, and the Cretaceous system. These 

 rocks occur in all parts of the world, and abound in 

 remains of plants and animals now entirely extinct. 



I. — Trias, or, New Red-Sandstone Group. 



This is a marine formation, composed of varie- 

 gated marls and sandstones, conglomerates, and 

 limestones, frequently of a red colour, with exten- 

 sive deposits of gypsum and rock salt, and contain- 

 ing numerous brine springs. 



