176 THE GEOLOGICAL SUCCESSION 



most prominent. The Belemnites also abound, creatures 

 resembling the cuttle fish. The polyparia were very abun- 

 dant in the seas of the Oolitic period. Whole rocks are 

 entirely formed out of the remains of these animals. The 

 crinoids are not quite so numerous as in former ages ; but 

 star-fishes abound, and an extraordinary and beautiful va- 

 riety of sea urchin with large spines, the Cidaris coronata. 

 The animals of the Cretaceous period bear the same gene- 

 ral characters as those of the Oolitic, but with a more 

 marked tendency towards existing forms. It is true that 

 there is ^ome evidence of the existence of mammalia, but 

 they are few and insignificant. The only traces of mam- 

 malia consist of two or three marsupial animals — creatures 

 allied to the opossum. Throughout the whole of this im- 

 mense period of time, the class reptilia was the preponde- 

 rating form. The lower forms of both animal and vege- 

 table life attained a gigantic development. " With flocks of 

 pterodactyles flying in the air, and shoals of no less mon- 

 strous ichthyosauri and plesiosauri swarming in the ocean, 

 and gigantic crocodiles and tortoises crawling on the shores 

 of the primeval lakes and rivers ; air, sea, and land must 

 have been strangely tenanted in these early periods of our 

 infant world."* 



In those geological periods immediately following the 

 deposition of the chalk, the last formation of the secondary 

 age, the marin^ or amphibian reptiles are replaced by nu- 

 merous mammalia of enormous size. These periods com- 

 prise the difierent tertiary formations. This era has, 

 therefore, been called the Age op Mammals. The animal 

 remains contained in these formations,, strikingly approxi- 

 mate in organic development to the species now living. 



* Dr. Buckland. 



