120 THE STORY OF THE EARTH. 



notched like those of dogs, seals, and other car- 

 nivorous mammals. There are also types which 

 have tuberculate crowns to the grinders adapted 



for crushing food, during which process the crowns 

 become ground down, as among Insectivora and 

 Rodents. 



There are in the genus Dicynodon only two teeth 

 in the upper jaw, which correspond to the tusks 

 the walrus. 



In Pareiasaurus the surface of the skull is cov- 

 ered with an arrangement of bones which appears 

 to be identical with that seen in the Pabyrintho- 

 donts. Labyrinthodonts were formerly grouped 

 with the Amphibia, but may be closely related to 

 the AnomodontS. Pareiasaurus appear to be in 

 many ways transitional between existing reptilia 

 and mammalia; in so far as can be judged from 

 the skeleton. It is with existing marsupials and 

 Camivora, and hoofed or ungulate mammals that 

 the resemblances in the forms of the bones appear 

 to be closest. 



The Trias. 



A glance at a geological map of England and 



Wales shows that the Trias, which extends to the 

 south of the Pennine chain, between Nottingham 

 \ Staffordshire coal-field, rests un- 



formably upon the denuded edges of the Per- 

 mian and Carboniferous strata. Great changes 

 had taken place m the earth's surface after tho 



osition of the Permian ro< ks, and a commence- 

 • was made in the definition and uplifting ol 



ie Trias was laid down 



• its southern termination. 



I a I England the Trias comprises two b< 



I he 1' -\v er, named Punter, con 



