DESCRIPTION OF SPECIES. 



PP. 107 



Goniopteris eniarginata, 



" eleoraijs, . 



" longifolia, . , 



" arguta, . . . . 



" elliptica, . . . 



" oblonga, 



*' Newberriana, 



Cymoglossa obtusifolia, . . 



'• breviloba, . . 



" foriiiosa, . . . 



" lobata, . . . . 



Alethopteris Virginianu, . 



" aigas, . . . . 



Taeniojiteris Lescuriana, . 



Newberrviana, 



Rbacophyllum filiciforme, . . 

 " laciniatum, . . 



" lactuca, . . . , 



" speciocissimuui, 



Caulopteris elliptica, , 



gigantea, 



Sigillaria approxiniata, . . 



" Brardii, ... 



Cordaites crassinervis, . . 

 Rhabdocarpus oblongatus, 



Carpohtbes bicarpa, . . . 



" marginatus, . . 



Guilielinites orbicularis, . 



Saportaea grandifolia, 



" Salisburioides, 

 Baiera Virginiana, . . . 



Totals, 



107 



t? 



t 



Near to T. 

 muUinervis 

 Near to 7'. 



vitUita. 



. t. • . 



t 



Allied to 

 C. peAtiqerd. 

 Allied to C. 

 macrodiscus 



t 



22 



Allied to 6. 

 permianus 

 Go p. 



Allied to 

 B. digitala. 



28 



Before proceeding to an analysis of the table, and the 

 conclusions to be derived from it, we may properly decide 

 what sort of evidence we shall admit to determine the age 

 of a formation, and what is the relative value of that de- 

 rived from each source. So far as the question of relative 

 value is concerned, this can only arise in the case where we 

 have to consider the contiicting evidence of different classes 

 of organisms, for no one will deny that the life of a period, 

 if well represented, is of the highest value in determining 

 questions of age. For our purpose we need only to con- 

 sider the claims of the three classes usually most relied 

 upon by Palaeontologists, viz : Marine Mollusks, Verte- 



