262 PALEONTOLOGY : FOSSIL ORGANIC REMAINS. 



Alexander Brongniart, that we owe the establishment of ("he 

 science of fossil geology, by the successful combination of 

 zoological types with the order of superposition and the 

 relative age of strata. The oldest sedimentary strata pre- 

 sent to us, in the organic remains which they contain, a 

 variety of forms occupying very different gradations in the 

 scale of progressive development. Of plants, we find a 

 few Fuci, Lycopodiacese which were perhaps arborescent, 

 Equisetacese, and tropical ferns : but of animals we discover 

 a strange association of Crustacea (including Trilobites with 

 reticulated eyes), Brachiopoda (Spirifers, Orthis), elegant 

 Sphseronites allied to Crinoidea, ( 2 ") Orthoceratites of the 

 family of Cephalopoda, and numerous corals ; and, mingled 

 with these animals of inferior order, we already find in the 

 upper beds of the silurian system fish of singular form. 

 The family of Cephalaspidse, animals of which the head was 

 defended with large bony enamelled plates, and fragments 

 of one genus of which (the Pterichtys) were long mistaken 

 for trilobites, belong exclusively to the devonian forma- 

 tion (old red sandstone) ; this family constitutes, according 

 to Agassiz, as distinctly marked a type in the series of fishes, 

 as that which includes the Ichthyosaurus and Plesiosaurus 

 among reptiles. ( 30 ) Goniatites, belonging to the tribe 

 of ammonites, ( 301 ) also begin to shew themselves in the 

 limestone, and in the greywacke of the devonian formation; 

 and even appear in the lower silurian strata. 



In respect to invertebrate animals, no very clear relation 

 has yet been recognised between the age of rocks, and the phy- 

 siological gradation of the species which they contain : ( 302 ) 

 but this relation manifests itself in a very systematic manner in 

 vertebrate animals. In these, the most, ancient forms, as 



