OF TRILOBITES. 7 



they occur, it may be well to give, in a short tabular form, the Palaeozoic arrangement fol- 

 lowed in this work, with the distribution of the Trilobites as to maximum and minimum in 

 these zones. 



The Palaeozoic groups are nearly those adopted of late years by our leading geologists. 

 For the determination of the lower ones we are almost equally indebted to Murchison and 

 Sedgwick, and their labours since 1831 have now become the common property of the 

 scientific world. 



GROUPS. 



TRILOBITES. 



C2 



> 



tt 



O 



z -< 



2 

 o 

 a 



None. 



UPPER PALAEOZOIC 



r Magnesian Limestone, &c 



Permian { Pontefract Sandstone 



{Upper Coal Measures -i 

 Lower Coal Measures I Extremely rare. 

 Millstone Grit J 



{Yoredale Rocks "l 

 Mountain Limestone I Three genera only. 

 Carboniferous Slate J 



fed 



o . 



> 



Upper Devonian . 

 Middle Devonian. 



Lower Devonian . 



MIDDLE ? PALAEOZOIC. 1 



r Pilton and Marwood group (Upper -| 



J Old Red Sandstone) I Few genera ; few species. 



t Petherwin group J 



[ Plymouth group (Middle Old Red 

 Sandstone) 



{Linton and Fowey group (Lower Old -» 

 Red Sandstone) ^. p ew g enera ; many species. 

 Ledbury Shales (Passage Beds) J 



Few genera ; many species. 



Ludlow 



►■d 

 *d 

 fed 

 W 



2? -I 



a 

 fed 



H 



Wenlock. 



May-hill. 



LOWER PALJEOZOIC. 



{Upper Ludlow (Murchison) 

 Aymestry and Lower Ludlow (Mur- 

 chison) 



r Wenlock Limestone (Murchison) ... 



I Wenlock Shale (Murchison) 



] Woolhope Limestone (Murchison) ... 



<- Denbighshire Grits (Sedgwick) 



[ May -hill Sandstone (Sedgwick); Up- 

 per Llandovery (Murchison) 



Few genera ; abundant species. 



> Many genera ; abundant species. 



Many genera and species. 



1 This term is introduced in deference to published authorities. But the Upper and Middle Palaeozoic 

 groups are together only equivalent to the Lower, and might well be all included under the one term 

 " Upper Palaeozoic." 



