154 PICTURESQUE SKETCHES 



localities of that kind, and also of the predatory and 

 voracious races that pursue and devour them. Let 

 us turn now to the consideration of the animals of 

 higher organization, and endeavour to learn from their 

 remains, so far as they are handed down for our in- 

 vestigation, how far they will help us to determine 

 the problem of the true nature of the lias fauna. 



Reptiles, as they exist at present, are convenient- 

 ly grouped into five principal subdivisions, character- 

 ised respectively by the crocodiles, the lizards, the 

 tortoises and turtles, the serpents, and the frogs. 

 Among these, there are none which are so organized 

 that the open sea can be called their chief habitation, 

 none are provided with any apparatus by which they 

 can support themselves in the air like birds, and none 

 exhibit a distinct connecting link with the quadru- 

 peds, by the possession of such locomotive organs 

 as raise them above the ground in any proportion 

 to their absolute magnitude. The whole number 

 of species of these animals now known is also not 

 very considerable, and they can hardly be said to 

 perform a part of great importance in the eco- 

 nomy of the globe.* We have already stated, in 

 the account of the palseozoic period, that interesting 



* Animals of this kind appear to be chiefly abundant, and to attain the 

 largest dimensions, in those hot districts, chiefly intertropical, where the 

 banks of large rivers are occasionally overflowed, and where extensive 

 tracts not much raised above the sea level are sometimes clothed with rich 

 vegetation, sometimes consist of bare hard clay, and sometimes of soft mud. 

 The larger crocodiles and alligators especially inhabit the muddy districts : 

 in the rainy season they appear and range about, preying on the various 

 animals that approach the water ; but in the hot dry season they retire, 

 and become so coated with hardened mud, as even to escape being seen 

 by the traveller. 



