330 



FOSSILS OF UPPER CRETACEOUS BEDS. 



[Ch. XVII. 



With these mollusca are associated many Bryozoa, such as Eschara 

 and Escharina (figs. 316, 317), which are alike marine, and, for the 

 most part, indicative of a deep sea. These and other organic bodies, 

 especially sponges, such as Ventriculites (fig. 318), are dispersed in- 

 differently through the soft chalk and hard flint, and some of the 

 flinty nodules owe their irregular forms to enclosed sponges such as 

 fig. 319 <x, where the hollows in the exterior are' caused by the 

 branches of a sponge, seen on breaking open the flint (fig. 319 b). 



The remains of fishes of the Upper Cretaceous formations consist 

 chiefly of teeth of the shark family of genera, in part common to the 

 tertiary, and partly distinct. To the latter belongs the genus Ptycho- 

 dus (fig. 321), which is allied to the living Port Jackson Shark, Ces- 

 tracion Phillipiii, the anterior teeth of which (see fig. 322 a) are 

 sharp and cutting, while the posterior or palatal teeth (6) are flat, and 

 analogous to the fossil (fig. 321). 



Fig. 322. 



Pig. 321. 



Palatal tooth of 



Ptychodtos decv/rrens. 



Lower white chalk. 



Maidstone. 



Cestraeion PMllippi ; recent. 

 Port Jackson. Buckland, Bridge-water Treatise, pi. 2T d. 



But we meet with no bones of land animals, nor any terrestrial or 

 fluviatile shells, nor any plants, except sea-weeds, and here and there a 

 piece of drift-wood. All the appearances concur in leading us to con- 

 clude that the white chalk was the product of an open sea of consider- 

 able depth. 



The existence of turtles and oviparous saurams, and of a Pterodactyl 

 or winged lizard, found in the white chalk of Maidstone, implies, no 

 doubt, some neighboring land ; but a few small islets in mid-ocean, 

 like Ascension, formerly so much frequented by migratory droves of 

 turtle, might perhaps have afforded the required retreat where these crea- 

 tures laid their eggs in the sand, or from which the flying species may 

 have been blown out to sea. Of the vegetation of such islands we 

 have scarcely any indication, but it consisted partly of cycadaceous 

 plants ; for a fragment of one of these was found by Capt. Ibbetson 

 in the Chalk Marl of the Isle of "Wight, and is referred by A. Brong- 



