170 



The existence of this class might easily have escaped 

 attention, for it is maintained from not more than ten 

 fragments of the jaws, and a few detached bones from 

 Stonesfield, and from the more nnmerons remains, very 

 recently collected in Dorsetshire, out of a bed only about 

 five inches thick, in the Middle Perbeck or Wealden 

 strata. The animals to which they belonged were of 

 very small dimensions, most of the jaws being under an 

 inch in length. The Oolitic system represents a long 

 and interesting era : it has probably received a longer 

 and more constant attention than any other, rewarding 

 the researches of Palaeontologists with a profuse variety 

 of extinct creatures. The chief characters of the forma- 

 tion is the extraordinary development of the Cephalo- 

 poda and Reptilia, the latter so numerous, that the era 

 has been styled the " Age of Keptiles." 



In the Cretaceous system is a similar Fauna to that of 

 the Oolite, but ^vdth generic and specific characters pecu- 

 liar to itself. It is reported that there have been traces 

 of Birds and IMammalia discovered, but we may consider 

 that very doubtful. The sj^stem seems to have been a 

 deep-sea deposit, some of its members being almost en- 

 tirely composed of the cases of Foramiuifera. 



Previous to the Cretaceous era all the Fishes were of 

 Placoid and Ganoid types ; now, the Ctenoid and Cycloid 

 orders are observed. Afterwards, in the Cainozoic period, 

 they became far more numerous. At the end of the Cre- 

 taceous epoch, which is also the termination of the Meso- 

 zoic period, an elevation of the strata took place, which 

 probably considerably modified the geography of sur- 

 rounding lands and continents. There was also a total 

 change or substitution of the Fauna : considering 

 these two circumstances together, the relation between 

 them is very evident. In England we see the chalk 

 clifis, not only elevated, bnt thrown into a vertical posi- 



