171 



tion; aud also find the whole series of Mesozoic types 

 destroyed, in consequence of convulsions, and elevations 

 of the sea bottom. 



After the close of the Mesozoic period, a long interval 

 seems to have elapsed before the lowest Cainozoic strata 

 were deposited unconformably upon the deranged Cre- 

 taceous rocks. The connecting links, though absent in 

 the British Islands, are partially displayed on the conti- 

 nent. Further investigations may, perhaps, hereafter 

 enable us to ascertain the nature of great organic 

 changes, coincident with great subterranean movements; 

 for it cannot be too strongly impressed upon the mind, 

 that these breaks in the continuity of the strata only 

 exist over a certain area, or over regions subject, directly 

 after formation, to extraordinary elevatory movements ; 

 and that distant places may afford evidence to fill up the 

 missing links, and render more perfect one great geologi- 

 cal liistory, of which oru- systems are mere arbitrary 

 divisions. If convulsions and upheavals of the earth's 

 surface account for the destruction of all prevailing forms 

 of life existing at the time in a particular region, the occur- 

 rence of very different types in the succeeding deposits 

 is rather the index of gradual changes during the inter- 

 val, that sedimentary dej)Osition had been suspended, 

 than of an extraordinary vitality of creative energy in 

 the sudden introduction of new species. 



Referring to the Upper Palaeozoic period, we find Placoid 

 and Ganoid Fishes most conspicuously developed. In 

 the ]\Iesozoic, Reptiles were more strikingly prominent, 

 performing their functions in the sea, Enahosauria ; upon 

 the land, Dinosauria; and in the air, Pterosauria ; but 

 in the Cainozoic, is a still greater advance in creation. 

 Birds and Mammalia occupying the position held by the 

 Reptiles of the former period. 



'J'he fauna of the Cainozoic period is represented by 



