334 LEAVES FROM THE 



found in formations anterior to, and including the chalk ; 

 whilst the true crocodiles, with a short and broad snout 

 like the alligator, appear for the first time in strata of 

 the tertiary periods, in which the remains of mammalia 

 abound. 



Though neither crocodile nor alligator exists in Europe, 

 nor ever, I believe, has existed there since that quarter 

 of the globe was peopled, there was a time when this 

 now temperate island must have teemed with animals 

 only able to exist in warm latitudes, and when its hotter 

 clime presented a congregation of all the crocodilian 

 forms now so widely scattered and separated. What 

 geographical changes has the world undergone since that 

 time! How different was the face of this fair island 

 before the eocene deposits were formed ! 



At the present day the conditions of earth, air, water, and 

 warmth, which are indispensable to the existence and propagation 

 of these most gigantic of Uving saurians, concur only in the tropical 

 or warmer temperate latitudes of the globe. Crocodiles, ga vials, 

 and alligators now require, in order to put forth in fvdl vigour the 

 powers of their cold-blooded constitution, the stimulus of a large 

 amount of solar heat, with ample verge of watery space for the 

 evolutions which they practise in the capture and disposal of their 

 prey. Marshes with lakes — extensive estuaries — large rivers, such 

 as the Gambia and Niger, that traverse the pestilential tracts of 

 Africa — or those that inundate the country through Avhich they 

 run, either periodically, as the Nile for example, or with less regu- 

 larity, like the Ganges, or which bear a broader current of tepid 

 water along boundless forests and savannahs, like those ploughed in 

 ever-varying channels by the force of the mighty Amazon or 

 Oronooko, — such form the theatres of the destructive existence of 

 the carnivorous and predacious crocodilian reptiles.* 



Well may the gifted Professor ask. What must have 

 been the extent and configuration of the eocene con- 

 tinent which was drained by the rivers that deposited 

 the masses of clay and sand, accumulated in some parts 



* Owen's History of British Fossil Reptiles, now in course of 

 publication. 



