164 



carbonate of Lime, often soft and ptilverulent, and containing 

 large numbers of the minute shells of Foraminifera, beautiful 

 star-fishes, and Echmidce, in admirable preservation, and with a 

 large assemblage of Mollusca. It is well exposed in the Isle of 

 Wight, Kent, and Sussex, and at Mamborough Head, Yorkshire. 

 The White Chalk forms the Graie hlanche of the French, and the 

 Etage Senonien of D'Okbignt. 



Palseontologically considered, the Cretaceous period presents 

 certain remarkable characters, which appear to indicate that it 

 was a great marine formation deposited far away from land. 

 Tor although mammalia and birds are found in the Jurassic 

 rocks, no remains of either of these classes, with the exception 

 of the bone of a bird from the Upper Greensand, have been as yet 

 discovered in any formation of the Cretaceous group. The 

 Dinosaurian, Enalosaurian, and Pterodactyhan reptiles, which 

 played so important a part in the Jurassic period, continued 

 to maintain a high development in the Cretaceous, but towards 

 its close they all became extinct. Fishes, anterior to the 

 Cretaceous era, were represented by ancient forms of the 

 Placoid and Ganoid orders; with the commencement of 

 the Cretaceous formations, the Teleosteian or true bony fishes 

 (including the Ctenoid and Cycloid orders, containing 

 three-fourths of the eight thousand known species of living 

 fishes) appear for the first time, when many of the preceding 

 fossil genera of the two first orders representing the most 

 ancient types of ichthoidal structure had become extinct. 



Among the Mollusca, the great family of AmmoniUdce 

 continued to flourish in vast numbers, exhibiting remarkable 

 forms that are special to this period. AH these became extinct 

 with its close, not one representative of its long line of ancestry 

 having survived in the seas of the Tertiary epoch. One singular 

 family of the Conchifera, the Budistidce, which present so many 

 curious forms in certain superior Cretaceous rocks, are altogether 

 special to them. 



The PoLYzoA have a very large number of beautiful forms in 

 the White Chalk, which are well figured in Dixon's Sussex. 



