xlvi PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



under and into the base of the Carboniferous series. The base, 

 therefore, of this Old Red Sandstone series is, it appears, conformable 

 to the Ludlow rocks, and the top to the Carboniferous, and there are 

 two strong unconformities between. The geological succession is 

 therefore singularly broken and incomplete. I agree with Mr. Jukes 

 that the classification of the Old Red strata requires to be remodelled ; 

 but, however this may be, it is clear, from the long-continued denuda- 

 tions that preceded each unconformity, that enormous gaps exist in 

 the recognized scale of British Old Red strata, lapses of unrepre- 

 sented time, the results of which we partly find in changes of life. 



Devonian Rocks. — Excepting that they are arranged in a given 

 order of superposition, there is little to be said respecting the 

 relation of the fossils to the stratigraphical relations of the Devonian 

 rocks of the south-west of England. When, many years ago, that 

 area was mapped, extreme analyses in geological surveying had 

 scarcely been introduced ; and in that country, consisting so largely 

 of granite and gneiss, contorted greywacke and limestone, no one 

 attempted on maps to split up the Devonian series into distinct sub- 

 formations. So exceedingly disturbed are the strata, that without 

 a new survey it is to this day impossible to say what unconformities 

 may or may not exist among its members. Neither, till the country 

 is remapped, is it possible to make out accurately the exact zoological 

 relations of the subdivisions ; and the data I now present are only 

 approximate, being the result of an examination of Devonian lists 

 with Mr. Salter, who placed his intimate knowledge of the ranges 

 of palaeozoic forms at my disposal. 



Eirst, then, the Devonian fossils are distinct from those of the 

 Silurian rocks of the district — a circumstance easily accounted for 

 when we know that they lie directly and unconformably on Lower 

 Silurian strata. 



This, therefore, makes it impossible to prove that in Devon or Corn- 

 wall the lowest Devonian rocks exist. In North America, where 

 such beds lie directly on Upper Silurian strata, it is plain that the 

 latter suffered extensive erosion before the deposition of the former, 

 this physical break being accompanied by a marked break in organic 

 succession. There is thus reason to believe that, if our Upper Silu- 

 rian strata were in contact with the Lower Devonian rocks of Devon 

 and Cornwall, the same broken relations would exist between them ; 

 for, of the several hundreds of Upper Silurian forms, it is said that 

 only about six species occur in the Lower Devonian rocks, perhaps 

 not more than 1 per cent. Thus, therefore, we have a zoological 

 break, all but total, between two formations, accompanied probably 

 by a vast lapse of time unrepresented by any strata in Devonshire, 

 and only possibly represented by the so-called unfossiliferous Lower 

 Old Red Sandstone of Ireland, Scotland, and Wales. 



There being, in Mr. Salter's opinion, no marked zoological line 

 between our Lower and Middle Devonian rocks, I have massed them, 

 and divided the series as follows. 



1. Marwood and Pilton beds = the Coomhola Grits of Mr. Jukes 

 and Carboniferous Slate of Sir R. Griffith. 



