I.] 



IMPORTANCE OF PALEONTOLOGY. 



To those readers who may not be geologists, the following 

 table of the leading divisions into which the strata of the earth's 

 crust have been divided will probably be advantageous. Com- 

 mencing with the highest beds, the series will run in descending 

 order as follows, viz. : 



Tertiary. PLISTOCENE. Cavern and River Deposits. 



PLIOCENE. The "Crags" of the East Coast. 

 MIOCENE. (Eningen beds of Baden. 

 OLIGOCENE. Gypsum of Paris Basin; Phos- 

 phorites of Central France. 

 EOCENE. London Clay. 

 Secondary. CRETACEOUS. Chalk, Upper Greensand, Gault, 



Lower Greensand, and Wealden. 

 JURASSIC. Purbeck beds, Portland series, Kim- 

 meridge Clay, Coral Rag, Oxford 

 Clay, Great Oolite, Stonesfield 

 Slate, Inferior Oolite, Lias. 

 TRIASSIC. New Red Sandstone of Cheshire. 

 Paleozoic. PERMIAN. Red Marls. 



CARBONIFEROUS. Coal-Measures and Moun- 

 tain-Limestone. 

 SILURIAN. 

 ORDOVICIAN. 

 , CAMBRIAN. 



Older rocks of Wales and the 

 Lake-District. 



Before attempting to draw any conclusions as to the former 

 configuration of the surface of the earth from the 



,. . .,,...,... Inequality in 



distribution of the animals now inhabiting its dif- the Ages of dif- 



ferent countries, it is essential to understand that 

 the different classes into which vertebrate animals 

 are divided (and these only will be taken into consideration in the 

 present volume) have a very different past history; the lower 

 groups, such as fishes, reptiles, and amphibians being much older 

 types than mammals and birds, and having attained their maximum 

 development at a time when the two latter formed but a small 

 minority of the earth's population. 



There is a considerable probability that at least a very 

 large proportion of the animals that have populated the globe in 



