188 THE WOKLEV 



mammalia and carnivora< of species and genera, both recent anej' 

 extinct. 



2. THE TERTIARY SYSTEM. An extensive series comprising 

 many isolated groups of marine, and laccistrine, or lake formed 

 deposits, characterized by the remains af animals and vegetables,, 

 the greater portion of which are extinct. Volcaaoes of great ex- 

 tent were in activity during this epech. Mr. Lyell subdivides 

 this series irfto the pliocene, or more recent; the wiocene, less re- 

 cent; and the eocene, dawn of recent; according to ehe percentage 

 of recent shells contained in each. 



Secondary Formations* 



3. THE CHALK OR CRETACEOUS SYSTEM. A marine formation ^ 

 being the bed of an ancient sea, comprising limestones, sand- 

 stones, marls, and clays, and abounding in the remains of zoophy- 

 tes, molusca, cephalapoda, fishes &c* drifted wood, and marine 

 plants, with crocodiles, turtles and other, now extinct reptiles,, 

 also birds. 



The chalk formation embraces several beds or distinct strata, 

 thus, we have the upper chalk with flints, and the lower without; 

 the chalk marl, the firestone, the gait or stiff blue, or black clay, 

 abounding in shells, the shankHn or green sand. 



4. THE WEALDEN. From the German icald, a wood., th. 

 whole tract so called in England having been once a dense foresL 

 This formation is the only known secondary fluviatile, or river 

 formed deposit. It is a fresh water formation, evidently the de- ' 

 posit of some enormous ancient rivers, its fossil remains being 

 the spoils of river and land, it is characterized by the remains of 

 enormous and peculiar reptiles, namely the iguanodon, hylaeosa- 

 rus, megalosaurus, plesiosaurus, crocodile, turtle, &c.; of ter- 

 restrial plants, fsesh water shell-fish, and birds. The group 

 called the Wealden is composed of beds of stiff blue clay, with 

 beds of shelly limestone, called Sussex marble, beds of sands and 

 sandstones as found at Hastings in England, and the clays, sand- 

 stones, and shelly limestones, as found in the Isle of Purbeck, 

 called Purbeck marble, 



