Life Changes on the Globe. 331 



only one extinct order of Amphibia, the Labyrinthodonts ; but 

 there are at least four distinct extinct orders of Reptilia, viz. the 

 Icthyosauria, Plesiosauria, Pterosauria, Dinosauria, and perhaps 

 another or two. There is no known extinct order of birds, 

 and no certainly known extinct order of Mammals, the ordinal 

 distinctness of the ' Toxodontia' being doubtful :" — 



' The two highest groups of the Annulosa, Insecta and Arach- 

 nida, are represented in the Coal either by existing genera or by 

 forms differing from existing genera in quite minor peculiarities. 



" Turning to the Vertebrata, the only palaeozoic Elasmobranch 

 Fish of which we have any complete knowledge is the Devonian 

 and Carboniferous Pleuracanthus, which differs no more from exist- 

 ing Sharks than these do from one another. 



"Again, vast as is the number of undoubtedly Ganoid fossil 

 Pishes, and great as is their range in time, a large mass of evidence 

 has recently been adduced to show that almost all those respecting 

 which we possess sufficient information are referable to the same 

 subordinal groups as the existing Lepidosteus, Polypterus, and Stur- 

 geon ; and that a singular relation obtains between the older and 

 the younger Fishes ; the former, the Devonian Ganoids, being 

 almost all members of the same suborder as Polypterus, while the 

 Mesozoic Ganoids are almost all similarly allied to Lepidosteus." 



With these facts before us, how are we justified if we retain the 

 phraseology of the scientific convulsionnaires, or impute to the 

 operations of nature, jerks, cataclysms, and violence, which are 

 not evidenced by external facts, and which are highly improb- 

 able upon a priori grounds ? 



It is curious that the theories of spasmodic geology have 

 readily allied themselves with development speculations, which, 

 if valid in any shape, must demand such enormous periods of 

 time, and such gradual processes of modification, as to have 

 more real affinity with the philosophy that Lyell has traced. 

 In common with most other physiologists, Professor Huxley 

 comes to the conclusion that " positive evidence fails to de- 

 monstrate any sort of progressive modification towards a less 

 embryonic or less generalized type in a great many groups of 

 animals of long-continued geological existence." In such 

 groups he finds abundant evidence of variation — none of what 

 is ordinarily understood as progression/-' and he adds, u if the 

 known geological record is to be regarded as even any con- 

 siderable fragment of the whole, it is inconceivable that any 

 theory of a necessarily progressive development can stand." 

 If, however, the plan of creation involves progressive modifica- 

 tion, then even what we commonly understand by " geological 

 eras" will appear brief spaces of time when compared with 

 the enormous periods during which modifications have taken 

 place, and <e the conclusion will inevitably present itself that the 



