168 



fishes lead us to the conclusion that this rarity was real, 

 and that air-breathing animals formed but a small propor- 

 tion of the entire fauna. 



The organisms of the mountain limestone and of the 

 coal-measures, differ essentially to the extent that might 

 be expected of marine and fresh-water deposits. In 

 the latter we find the earliest Insecta of the orders Cole- 

 optera and Neuroptera. 



In the Permian system the reptiles are more numerous, 

 though still rare. No class of the animal kingdom is pre- 

 sent that is not also in the Carboniferous system, and no 

 invertebrated class not also found in Silurian strata, 

 while in each the number of observed species is conside- 

 rably less. This system closes the Palteozoic j)eriod. 

 Afterwards the Flora and Fauna become so changed, that 

 most of the generic types, and certaiul}^ all the species, of 

 both plants and animals appear to have been replaced by 

 new ones. All nature assumes a new aspect, and reveals 

 as it were a new creation. In the fishes this change is 

 very striking, in the Avell-known heterocercal and homo- 

 cereal forms, as they emerge from the Permian to the 

 Triassic systems. 



There can be little doubt but that these great organic 

 changes were intimately connected with the comprehen- 

 sive disturbances that marked the close of the Palaeozoic 

 period. The complicated upheavals of the Carboniferous 

 and Permian strata seem to have chiefly occurred at this 

 time ; and when we consider the gigantic nature of these 

 convulsions, we cannot be surprised at the scanty traces 

 of ancient life afforded to our view in the succeeding 

 Triassic system. The tract of country in England occu- 

 pied by the Trias or New Red Sandstone is as extensive 

 as that of any other; yet the paucity, and often total 

 absence, of organic remains is remarkable. The diffusion 

 of per-oxide of iron through the waters, and the unstable 



