366 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 22, 



believe that a much closer analogy between the Silurian series of 

 Bohemia and Britain can be set up than that which M. Barrande has 

 established by a very good general identification of his rocks with my 

 Upper and Lower Silurians. And although, as before said, I think 

 that, in Bohemia, the Llandeilo zone can be distinguished from the 

 Caradoc zone, it will be impracticable so to define other details as to 

 say that any one bed of the Bohemian series is the equivalent of 

 one of our British Lower Silurian subformations. 



Again, in the Upper Silurian rocks, though the limestones or 

 upper portion of the * E ' of Barrande are clearly identifiable with the 

 Wenlock limestone, it does not follow that the shale beneath it 

 is equal to the Wenlock shale, merely because the mineral character 

 of the two rocks and the order of superposition agree. Judging 

 from the organic remains, M. Barrande may, I think, possibly be 

 induced to form a new group, and unite this shale with his D 5 , or 

 next underlying bed, and thus represent our Llandovery rocks. 



On this point I am disposed to be guided by the opinion of Mr. 

 Salter, who has taken great interest in the question of the Colonies ; 

 and he thus wrote, in June 1860, to Sir Charles Lyell : — " I regard at 

 present the Colonies, with the beds called Lower Silurian over them, 

 and the base of Etage E (Graptolite-bearing schists and trappean 

 beds), as equivalent to the Llandovery rocks, under an aspect different 

 from that which they present in Scandinavia and Britain." This 

 view, which Mr. Salter still maintains, he strengthens by assuring 

 me that the fauna of the Colonies consists chiefly of about 65 

 species (Barrande), of which 5 are peculiar, 2 are common to D 4 , or 

 Caradoc and Wenlock, and 58 are Wenlock forms.* 



In the uppermost Silurian rocks a few Ludlow types only are 

 mixed with many forms quite peculiar. It is therefore impracticable 

 to define the Bohemian subdivisions into Lower Ludlow, Aymestry 

 Limestone, Upper Ludlow, and Passage-beds, as attempted in the 



* On this head Mr. Salter has furnished me with the range of certain striking 

 Bohemian genera and species, as they occur in Britain : — 



Bohemia. Britain. 



Cheirurus insignis Very like the Wenlock C. bimucronatus, 



but long known as a species in the Ca- 

 radoc of Bohemia. 



Cyphaspis The genus in England — Wenlock. 



Lichas The genus in England — Wenlock. 



Sphserexochus mirus Lower Silurian to Upper Silurian. 



Orthoceras originale ..... Upper Silurian. 



, V species. 



Cyrtoceras Grenus in England — Upper Silurian. 



Terebratula obovata Upper Silurian. 



reticularis ? Lower Llandovery to Upper Silurian. 



Spirifer togatus Species not yet recognized. 



Leptsena euglypha Lower Llandovery to Upper Silurian. 



Cardiola, 4 species. 



interrupta Lower Silurian ? to Upper Silurian. 



Favosites Gothlandica .... Lower Silurian to Upper Silurian. 



Graptolithus priodon .... Lower and Upper Silurian. 



Nilssoni Lower Silurian. 



Becki Lower Silurian. 



