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Ch. IX.] 



AT SUCCESSIVE GEOLOGICAL PERIODS. 



155 



anatomist to assign to them by no means a low place in the 

 piscine class. In short, a retrospect of the history of this 



class in 



o-eolooical time 'imparts/ according to Professor 



Owen, < an idea rather of mutation than of progression. 

 Reptiles.— No well-authenticated example of a reptile 



old as the Devonian has yet been 



occurring in strata so 



established^ and it was not till the year 1844, that some 

 representatives of the lowest division of this class, the am- 

 phibia, which are regarded by some naturalists as interme- 

 diate between reptiles and fish, were discovered m the^ coal 

 of Saarbruck. Since that period several 



enera of the 



Labyrinthodont family, some containing species of large size, 



and Britain. 



So late as 1865, four or five new genera of 



this family determined by Professor Huxley have been 

 added from the coal of Tipperary in Ireland. 



Some of 

 theseYave well-ossified bony skeletons, although they belong 

 to that sub-class which, like the frogs and newts, possessed 

 gills at some period of their existence, and were also marked 

 by other piscine characters. In rocks of later age, from the 

 Triassic to the Cretaceous inclusive, there is an extraordinary 

 profusion of reptile life, to which I shall have occasion to 

 allude again in the eleventh chapter. Some of the ordei 



*s 



especially the Dinosaurians, are of so high a grade as to be 

 more akin to the mammalia than are any reptiles of later date, 

 whether tertiary or living ; so that we have here an example 

 of a class which gradually advanced till it reached a culmi- 

 nating point, from which it has ever since been retrograding. 

 The period of the degeneracy or degradation of this class 

 seems to have coincided with that of the first appearance on 



1 • 



the globe of the placental, or most perfect of the mammalia. 



Scarcity of air-breathers in primary rocks. — Our infor- 



mation respecting the fossils of the oldest rocks, especially 



those anterior to the Old Eed Sandstone or Devonian 

 formation, is almost exclusively derived from strata of 



marine origin. 



mi 



always occupied, as it does now, nearly five parts in seven of 



* Owen's Paleontology, 2nd edit, p 



175. 



f See Elements of Geology, 6th Edi- 

 tion, p. 526 note. 



