ANNIVERSARY ADDRESS OF THE PRESIDENT. xlvii 



2. Upper Devonian strata. 



3. Middle and Lower Devonian. 



The result of an elaborate analysis from Tables prepared for the 

 purpose is, that of known Middle and Lower Devonian fossils there 

 are about 61 genera and 170 species ; and of these about 23 species 

 only pass into the Upper Devonian division, or about 13| per cent. 



The Upper Devonian beds yield about 30 genera and 70 species ; 

 and of these, 24 (or about 34 percent.) pass into the Marwood beds, 

 which in Devonshire have heretofore given about 31 genera and 65 

 species, of which 14 species, or about 21 per cent., pass into the 

 Carboniferous rocks. Judged by the imperfect data of mere per- 

 centages, it appears then that the Upper Devonian are less intimately 

 connected with the Lower Devonian than with the Marwood beds, 

 and that the Marwood beds are zoologically more nearly related to 

 the Upper Devonian than to the Carboniferous strata. In the south- 

 west of Ireland the Coomhola Grits and Carboniferous Slate pass 

 downward into Old Red Sandstone, and upward into Carboniferous 

 Limestone ; and they are considered by Mr. Jukes either to be the 

 lowest part of the Carboniferous series, or else to form a distinct 

 group together with the upper half of the Irish Old Red Sandstone, 

 which is stratigraphically quite unconnected with the' lower half. 

 Further, it must be remembered that for many years, in Devon and 

 Cornwall, Silurian and Devonian rocks were all massed together, and 

 called by one name. But we know that there must be an uncon- 

 formity discoverable between the Lower Silurian and Devonian rocks, 

 if properly searched for ; and analogy would lead us to expect, from 

 the strong breaks in organic succession, that the same broken strati- 

 graphical relations — lapses of unrepresented time — must exist 

 between the various members of the typical Devonian series, just as 

 they certainly occur in what geologists consider their equivalents, 

 the Old Red Sandstones of Scotland and of Ireland. 



Carboniferous Series. — I have already stated that, of 65 species 

 from the Marwood beds, only 14, or about 21 per cent., pass into the 

 Carboniferous rocks ; while, if we take the whole of the Devonian 

 series, only 11 out of about 240 species, or rather less than 5 per 

 cent., are common to the Devonian and Carboniferous ages. 



If we now analyse the divisions of the Carboniferous series, it is 

 not easy in Britain at present to get evidence of anything like uni- 

 versal unconformity of one part on another, though there are proofs 

 of local disturbances. Thus in South Wales, Lancashire, Derbyshire, 

 and Yorkshire, the Carboniferous series has generally been described 

 as conformable from bottom to top. It is true that in Lancashire 

 Mr. Hull suspects unconformity between his Middle Coal-measures 

 and the Gannister beds, and that Mr. Marcus Scott has shown an 

 unconformity in the Coal-measures of Coalbrook Dale. I have al^o 

 myself seen the Millstone-grit resting unconformably on the Moun- 

 tain-limestone of the Forest of Dean ; and overlaps of Upper on Lower 

 Carboniferous rocks take place in Scotland and almost everywhere. 

 But in spite of these cases, in a formation like the true Coal-measures, 

 which evinces frequent oscillation of level, it is at present difficult 



