638 



PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



It has been stated that 13 species are common to the Loiver Old 

 Bed Sandstone and the preceding Silurian rocks ; bnt our comparisons 

 are confined to the group of Fishes contained in the passage-beds 

 between the two formations, of which there are seven species ; and, 

 from the want of this group of vertebrata in our Lower Devonian 

 slates, it is negative evidence only for the British area. I doubt 

 not that both the Lower, or Lynton, and the Middle, or Ilfracombe, 

 beds will yet yield many species of fish, remains of which, but with 

 hardly determinable characters, are frequently found in the slates 

 on the north coast ; for we now have conclusive evidence of their 

 presence from bones and coprolitic debris *. 



The following Table contains those invertebrate species still retained 

 by many as common to the Silurian and Devonian rocks ; I place 

 the mark of interrogation against those I would reject as being very 

 doubtful : — 



Species. 



Silu- 

 rian. 



Low. 

 Dev. 



Mid. 



Dev. 



Up. 

 Dev. 



Favosites fibrosa? Goldf. 



Tentaculites annulatus ? ScMoth 



Atrypa reticularis, Linn 



■Si- 

 ■«• 



■Si- 





, var. aspera, Schloth 



Ctenodonta (Clidophorus) ovata? Sow. 

 Orthoceras imbricatum ? Wahl 



The 7 species of Fish-remains cannot he compared, as we are not 

 dealing with the Old Med proper of the Silurian area. 



With the exception, therefore, of the ubiquitous Atrypa reticularis, 

 which is undoubtedly common to the Silurian and Devonian Kocks 

 in England and Europe, I believe we have no rehable species con- 

 necting the two great life-periods, viz. the Silurian and Devonian. 



"Whilst comparing the relation of the Silurian to the Devonian 

 fossils, it would be as well to name (before we discuss critically) 

 those species which are said to occur as common to the Lower 

 Devonian rocks of the Lynton area and the so-called Carboniferous 

 Slate above or to the south, and to link the two areas together in 

 North Devon, and which have been referred to as one of the reasons 

 for relating them, though this has only been done through the ap- 

 parent similarity of the rock-masses of the two areas, and from the 

 general resemblance that the slates of North Devon bear to the 

 Coomhola and Carboniferous Slates of the South of Ireland. Pro- 

 fessor Jukes, in his paper f, states that at Lynton, in the Yalley of 

 Rocks, he '' was again among rocks belonging to the Carboni- 

 ferous Slate," and that the fragments of Brachiopoda and aU other 

 fossils seemed to be the same as those of Ireland. To all outward 

 appearance there is and may be similarity, as there is in most slaty 

 regions ; and the Croyde and Baggy Slates to the south in a few par- 



* Mr. Valpy's collection supplies this evidence. 

 t Quart. Journ. Greol. Soc. vol. xxii. 18G6, p. 350. 



