176 THE GEOLOGICAL SUCCESSION 



most prominent. The Belemnites also abound, creatures 

 resembling tbe 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 some 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 marine or amphibian reptiles are replaced by nu- 

 merous mammalia of enormous size. These periods com- 

 prise the different 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. 



