228 GEOLOGY. 



eye, but one wide wilderness stretched far away, varied 

 only by slight undulations. We may get some idea of 

 the nature of this scenery from some localities on our 

 earth, but none at all of its extent. Especially extensive 

 were the platforms in the earlier part of the Carbonifer- 

 ous age, for the beds of coal then laid down are found 

 to be much vaster in extent than those of the later coal- 

 measures. In this country these early beds cover a large 

 portion of the continent. Each of the successive plat- 

 forms of luxuriant vegetation, after having maintained 

 the same level for hundreds, or even thousands of years, 

 was submerged in water gradually (Hugh Miller thinks 

 in some cases suddenly), that each bed of coal might be 

 packed down with layers of rock above it. The wide 

 wilderness of vegetation thus became a wide waste of 

 waters. 



329. Animals. So highly charged with carbonic acid 

 gas was the atmosphere of the coal-making age, that an- 

 imals which require such air as we now have on the 

 earth could not exist. There were, therefore, no mam- 

 mals or birds, and none of the higher kinds of insects. 

 There were cold-blooded animals, as fishes and reptiles, 

 the latter finding their appropriate localities in the stag- 

 nant pools, swamps, and thick, damp forests of that age. 

 Cold-blooded animals live an inactive, lazy life, as com- 

 pared with the warm-blooded, and therefore do not re- 

 quire so much oxygen.* There was, of course, an abund- 

 ance of Mollusks, Crustaceans, and Radiates, especially 

 when the platforms were submerged, and the limestone 

 strata were forming. The tameness and monotony of 



* It would seem at first thought that the life of fishes is generally a 

 very active one ; but it is not so, for the fish needs to make but little 

 effort in its motions, for two reasons. First, it is of nearly the same 

 specific gravity with the element in which it moves, and is therefore 

 obliged to make but a slight effort in any upward movement. It is 

 in strong contrast with birds in this respect. Secondly, most fishes 

 have an air-bladder, which they can compress or enlarge at pleasure, 

 as they wish to fall or rise. See my Natural History, Chapter xx. 



