696 PKOCEEDINGS OP THE GEOLOGICAL SOCIETY. 



elevation of the land over the district traced ont. There is nothing 

 in the physical structure of the country to forbid this supposition, and 

 on palseontological grounds nothing to disprove it. No form of inver- 

 tebrate life can be pointed out, over this great area, that lived on 

 beyond the deposition of the passage-beds on the confines of the two 

 systems. The fishes and Poecilopod Crustacea (both of which are 

 allied to fresh water forms) are not known beyond the old margin ; 

 and those species of fish that do occur are sparingly found in the 

 corn stones of Hereford and South "Wales. 



Either, I believe, we must admit that the total extinction of the 

 Silurian species at the commencement of the deposition of the Old 

 Bed Sandstone was due to those conditions I have endeavoured to 

 trace, or that the marine Devonian series mu-st have been deposited 

 and accumidated in an area having little or no community with the 

 previously existing Silurian sea, but went on synchronously with the 

 Old Eed Sandstone, though in a different province, and under marine 

 conditions ; and we have not, I think, any great difiiculty in approxi- 

 mately determining the position and probable extent of that area. I 

 am disposed to believe that these marine Devonian strata were ac- 

 cumulated in a definite region, defined by a barrier which may have 

 existed south of the Mendip Hills, and continuous or parallel with 

 that range towards France and Belgium and the Rhenish provinces. 

 Physicists may yet determine this ; but it is south, or along the 

 course of the Bristol Channel north, of the Foreland, that, I believe 

 it may be determined, the equivalent strata in time, the marine 

 Devonian rocks, were deposited. In other words, the southern Bri- 

 tish equivalents of the Old Eed Sandstone (the Devonians) were 

 deposited in a different and marine area, whilst the typical Old Eed 

 Sandstones were being accumulated in an area to the north of the 

 prescribed barrier, and are of purely freshwater origin, the contour of 

 that area being governed by the previously existing and older 

 Palaeozoic Eocks : the base of the one is seen in the Silurian area ; 

 and its upper members under many aspects may be examined in 

 "Wales, Somersetshire, and Gloucestershire, and under a different con- 

 dition still in ISTorth Devon and Ireland. 



It is from the remarkable contrast and difference that exists in the 

 lithological and physical characters of the rock-masses of the typical 

 Old Eed Sandstone in its various localities as compared with what we 

 believe to be its representative and equivalent in time, viz. the Devo- 

 nian in North and South Devon and in the European areas, that 

 we are led to examine into the causes for so complete a discrepancy ; 

 and looking at the exact bearing and well-defined strike of this westerly 

 remnant of the North-Devon Devonian rocks under the waters of the 

 St. George's Channel, or Atlantic Ocean, I am led to believe that an 

 extensive coast-line or barrier existed to the north of what is now 

 the coast of West Somerset and North Devon, at Lynton, Porlock, and 

 Minehead, and thus construct a different geographical area or pro- 

 vince of deposition and accumulation for the fossihferous marine 

 Devonian series. This sea and area would appear to have been ex- 

 tensive, if we correlate and connect our beds with their equivalents 



