SILURIAN ERA. 



are here for the first time restored with something like 

 accuracy and life-like proportions. As already hinted, the 

 remains of fishes are but sparingly found in the uppermost 

 beds of the system j and it is still an open question with 



1, Pterygotus Acurrrinatus ; 2, P. Bilobus ; 3, Ceratiocaris (bivalved Crustacean). 

 From tlie Upper Silurian or Passage Beds of Lanarkshire. 



geologists, whether these are to be viewed as marking the 

 close of the silurian or the dawn of the devonian epoch. 

 For our own part, we accept them as part and parcel of the 

 silurian fauna; and though negative evidence forbids us in 

 the meanwhile to enter on our lists the remains of insects, 

 reptiles, birds, and mammals, there is nothing that militates 

 against the likelihood of their occurrence. On the contrary, 

 all analogy favours the supposition that the great types of 

 life radiate, molluscan, articulate, and vertebrate were 

 from the beginning contemporaneous on our globe, and that 

 it is to the minor modifications of the type, and not to the 

 type itself, we are to look for that gradation and progress 



