1869.] The Treasures of Sihiria. 31 



Dr. Bigsby gives us an imposing summary of tlie fauna of the 

 Primordial Zone in Europe and America, namely, 375 species in the 

 former, and 597 species in the latter region ; but his definition of 

 the formation is so extremely wide that it is difficult, from his 

 figures, to arrive at the real value of the fauna of the period in its 

 more restricted meaning. To prevent any misunderstanding, we 

 give the following comparative statements of what is usually 

 included in this formation, and of what the author includes within 

 its definition : — 



BEITAIN. 



BiGSBT. MUECHISON, BeLT, SaLTER, &C. 



Lower Llandeilo ) t o-i • e 



ci • 1 1 o, , ( Lower iSilurian of 



hkiddaw blates > .1 ., 



. . ^, I other authors. 



Aremg Group ) 



Stiper Stones \ rr j /^ 



Trimadoc Slate / Tremadoc Group. 



Linc^ula Flacks / Ffestiniog Group (Sedgwick). 



° ° \ Ma3nevian Group (Salter) . 



Harlech Grits Harlech Group. 



Llanberis Slates Llanberis Slates. 



CANADA AND UNITED STATES. 



Bigsby. Mukchison. 



IChazy Limestone (part). 

 Calciterous Sandstone. 

 Point-Le'vis Rocks. 



Lower Calciferous Group. 



Potsdam Sandstone | yPP""^ ^°;^^^°^ ^^°^P- 



( Lower Potsdam Group. 



St. John's Group. 



It is thus seen that Dr. Bigsby adds to what is usually termed 

 " Primordial " in Britain, the Lower Llandeilo of Murchison (the 

 Arenig Group and the Skiddaw slates being also of that age), 

 while his classification of the American rocks is still more compli- 

 cated. According to Sir R. I. Murchison the Lower Calciferous 

 Group is succeeded by (1) the Upper Calciferous Group, and (2) the 

 Quebec Group (including the Levis, Lauzon, and Sillery rocks), 

 both being regarded by him as of Llandeilo age ; and these are 

 again surmounted by the Chazy Limestone, which Sir Eoderick 

 refers to the base of the Caradoc formation, but part of which 

 Dr. Bigsby (as we have seen) also includes in the Primordial Zone ! 



With resjject to Bohemia there can be no difficulty, as there, of 

 course, the Primordial Zone is simply the Primordial Zone, the 

 " First [Fauna," the C.c.l of M. Barrande. The question is, 

 What are its equivalents in Britain and America? Or, to bring 

 the matter to a closer issue. Is Dr. Bigsby right in his extension 

 of the definition for Britain and America ? We cannot decide this 

 question ; but we are obliged by every rule of classification and of 



