ETHERTDGE DEVOXIAX ROCKS A?^D FOSSILS. 697 



in Belgium, and to the north, in the latitude of Diisseldorf and Ariis- 

 berg, [in the north of Rhenish Prussia,] and on the east to the 

 Taunus and Hundsriick ranges over the Coblentzian area, thence 

 south to Luxembourg, Mezieres, and the Ardennes &c., and con- 

 tinuously on, with interruptions, to the Boulonnais, under the Paris 

 basin, joining the narrow strip that reposes near Angers, Yannes, 

 and Quimper, in Brittany, upon the Silurian series. Patches of 

 Devonian rocks on the extreme north coast of Brittany would help 

 us to construct this southern boundary to the ^lid-European Devo- 

 nian deposits or area. 



It is not improbable that the Devonian rocks of the Pj^enees and 

 of the Asturias, which strike east and west parallel to the British 

 series, may have formed also a still more southerly extension of the 

 same. They occupy an immense area in the north of Spain and 

 south of France. On palaeontological grounds also the British, Irish, 

 Belgian, Prussian, South French, Pyrenean, and Asturian series may 

 have formed, and probably did form or constitute, a connected and 

 contemporaneous series of marine deposits — one definite hydro- 

 graphical area; for the facies of the fauna in all the districts is 

 the same. 



Somewhere, then, at no great distance south of the Mendip Hills, 

 I would suggest that an extensive barrier or ridge existed at the 

 time of the deposition of the Lower Old Red Sandstone, perhaps an 

 axis of depression synchronous with movements of elevation to the 

 north, in the Silurian area, which govenied the conditions of 

 the deposition of the Old Red Sandstone, and destroyed the 

 marine fauna at the close of the Silurian period. To the south 

 of this barrier, which severed the groups and cut off communication 

 with the northern area, were deposited the marine equivalents of the 

 Old Red Sandstone (the Lower and^liddle Devonian slates and lime- 

 stones) ; in other words, this barrier, let it have been what it may, 

 would produce two hydrographical areas — one marine, to the south, 

 the other freshwater, to the north, or in the Silurian area (Wales, 

 Herefordshire, Shropshire, Gloucestershire, &c.). A total change took 

 place in the marine fauna through its passage-series to the succeeding 

 and conformable Lower Old Red Sandstone, when the few Fish and 

 Crustacea in common to the two series almost, if not entirely, dis- 

 appeared ; and the vast accumulation of sandstones marks an epoch 

 and an area in one sense apparently lifeless ; for we have only two 

 or three species, and these land and freshwater, and found onlj- in 

 the upper part of the Old Red. 



The structure of North Devon does not aid us in one desired point, 

 there not being, as in the typical district, a recognizable base to the 

 Lower Devonian slates of Lynton, — the Silnrian, if there, being 

 deeply seated and beneath the Foreland sandstones. We cannot, 

 however, have any doubt, or hesitate to come to the conclusion, that 

 the red, grey, and variegated sandstones and grits that constitute 

 the structure of the country from the Foreland to Porlock, Mine- 

 head and Dunster, and the western side of the Quantocks belong in 

 time to this lower part of the Old Red Sandstone : neither can we 



