CHAP. XX. VERTEBRATA UNKNOWN IN OLDEST ROCKS. 403 



axiom in palaeontology, that reptiles had never existed before 

 the Permian or Magnesian limestone period, when at length, 

 in 1844, this supposed barrier was thrown down, and carbo- 

 niferous reptiles, terrestrial and aquatic, of several genera, 

 were brought to light; and discussions are now going on as to 

 whether some remains of an enaliosaur have not been detected 

 in the coal of Nova Scotia, and whether certain sandstones, 

 near Elgin in Scotland, containing the bones of lacertian, 

 crocodilian, and rhynchosaurian reptiles, may not be referable 

 to the "Old Eed" or Devonian group. 



Still, no traces of this class have j^et been detected in 

 rocks as ancient as those in which the oldest fish have been 

 found. 



As to fossil representatives of the ichthjic tj'pe, the most 

 ancient were not supjDOsed, before 1838, to be of a date 

 anterior to the Coal, but they have since been traced 

 back, first to the Devonian, and then to the Upper Silurian 

 rocks. No remains, however, of them or of an}^ vertebrate 

 animal have yet been discovered in the Lower Silurian strata, 

 rich as these are in invertebrate fossils, nor in the still older 

 primordial zone of Barrande ; so that we seem authorized to 

 conclude, though not without considerable reserve, that the 

 vertebrate type was extremely scarce, if not wholly wanting, 

 in those epochs often spoken of as "primitive," but which, if 

 the Development Theory be true, were probably the last 

 of a long series of antecedent ages in which living beings 

 flourished. 



As to the Mollusca, which affoi'd the most unbroken series of 

 geological medals, the highest of that class, the cejjhalopoda, 

 abounded in older Silurian times, comprising several hundred 

 species of chambered univalves. Had there been strong pre- 

 possessions against the progressive theory, it would probably 

 have been argued that\7hen these cej^halopods abounded, and 

 the siphonated gasteropods were absent, a higher order of 



