TELEOSAURIAN PERIOD. 179 



the latter now so valuable in Cleveland, Eskdale, and the Vale 

 of Mowbray, contain so much of sandy aggregates as to imply 

 the temporary influence of stronger but not violent currents. 

 Perhaps the depression which may be supposed to have gone on 

 generally and uniformly during the greater part of the liassic 

 accumulations, was at this epoch interrupted. The cause must 

 have been very extensive, for the marlstone beds are traced with- 

 out real interruption from Yorkshire into Somersetshire. 



In the liassic ocean nature was prolific of life. The sea was 

 too muddy for corals or Echinida to be plentiful ; in the lowest 

 calcareous bands Pentacriuites, and in the marlstone series both 

 Star-fishes and Pentacrinites, occur in great beauty, as at Staithes. 

 Belemnites, never seen in the older strata, now abound. Am- 

 monites, of many and quite different groups from the older forms 

 of involute Cephalopods, are equally plentiful. We have no Tri- 

 lobites, but many of the ordinary long-tailed Crustacea ; abun- 

 dance of fishes with symmetrical tails, and a great series of aquatic 

 reptiles, especially Ichthyosaurus, Plesiosaurus, and Teleosaurus, 

 in which the structures of Fish and Cetacea, of Turtle and Cro- 

 codile, are harmonized by nature into the same antique system 

 which includes the winged Pterodactyls. So perfect are the 

 skeletons of these mighty denizens of the old sea, that all their 

 structure is disclosed to the anatomist the very globe of the 

 eye is represented by its sclerotic plates the very skin and 

 dermal scuta can be traced, and the bones of the fingers counted 

 and compared with the component parts of the fin of the Whale, 

 the paddle of the Turtle, and the wing of the Bat (see the Mu- 

 seums at York, Whitby, and Scarborough). 



We may gather a condensed view of the rich variety of life of 

 this period in a tabular form. 



Marine life is represented by a few Algse and many animal 

 remains. 



Asterida. Dimyaria. 



Crinoidea, especially Pentacrinites. Monomyaria. 



Echinida. Brachiopoda. 



N2 



