ETHERIDGE DEYONIAIf EOCKS AND FOSSILS. 685 



holds good for Europe, so far as we know. Had such difference existed 

 over a vastly wider area, then the difference in the fossils of the Car- 

 boniferous and Devonian groups might be accounted for upon the 

 hypothesis that they were accumulated under very different condi- 

 tions physically and chronologically, and in a totally different area 

 or province ; but that the Upper Devonian series of [^Torth Devon, 

 and those of South Ireland, South Wales, and France (the Boulon- 

 nais), as well, perhaps, as the lower part of the Carboniferous (call 

 them what we will), were deposited synchronously, making what 

 reasonable allowance we please for locality, province, and difference 

 of nature of sea-bottom, there cannot, I think, be any reasonable 

 doubt ; but we cannot parallel the Lower and Middle grov/ps of the 

 Devonians here and on the continent with the Carboniferous under 

 any h\-pothesis. 



I by no means pretend to decipher, or to propose any different or 

 new theory relative to, the life-break that took place between the 

 Upper Silui'ian and Old Eed Sandstone, where in Shropshire, Here- 

 fordshire, &c. there is no unconformity or sudden break, their phy- 

 sical passage being uniform and complete, but accompanied by a total 

 extinction of the Silurian marine species, dependent, perhaps, upon 

 the relative positions of masses of land and water, causing the 

 marine condition of that area to become one of fresh water : all that 

 we can say amounts to this, that we cannot account for that com- 

 plete change, except through unconformity, of which we have no 

 actual evidence. The succeeding Old Red must have been depo- 

 sited in a rising and circumscribed area of greatly broken condition, 

 occupying a vast duration of time, sufficient to allow of the introduc- 

 tion of a new marine fauna to the south and east, either through 

 the. agency of dej^ression along a given line, east and west, about 

 the latitude of the Mendip Hills and the south of Ireland ; or a 

 barrier existed along the same line, against which the marine depo- 

 sits of the Devonian series were deposited, and that vdih. an ex- 

 extensive southern expansion. In no other way can we, I believe, 

 account for the physical change and zoological conditions of the ma- 

 rine Devonian rocks. 



Professor Jukes has shown a physical break between the two 

 members of the Old Eed Sandstone in Ireland, — the lower, of great 

 thickness, being conformable to the Ludlow group, whilst the upper 

 division, of some 4000 feet, rests unconformably on the Lower, 

 passing up and being conformable to the Carboniferous. We are not 

 yet certain what these may be the equivalents of in the South- 

 Welsh or, perhaps, North-Devon area. 



Mr. Geikie has shown the same for the Pentland and Lammer- 

 muir Hills, where, he states, the base of the Old Red Sandstone is 

 conformable to the Upper Silurian (Ludlow beds) ; a break occurs 

 between them in the red and yellow sandstones and associated 

 igneous rocks of the Middle, and then upon these another uncon- 

 formity of the Upper Old lied Sandstone, which at the top gra- 

 dually passes into the Carboniferous. There is, in fact, no division 

 of the British strata where the geological sequence or succession is 



