44 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



that the two areas were not under conditions ahke favourable for the 

 development of such a fauna. The answer to this is obvious ; — the 

 area over which a marine fauna such as we term Devonian comes in 

 succession on a Lower Silurian one is so vast and so varied in the 

 conditions which it indicates, compared with that in which an Upper 

 succeeds a Lower Silurian, that it is physically out of the question that 

 in the first-named area an Upper Silurian series of forms should have 

 been wholly excluded. 



With respect to the lower palaeozoic group of the French and 

 Southern European area, as known to us through the researches of 

 M. de Verneuil and Mr. D. Sharpe, there is enough to warrant a 

 comparison with our own typical Silurian series ; still it is clear that 

 at this early time there were two regions, — each having a facies of its 

 own, dependent on community of forms, and the limits of which lay 

 somewhere in the line of the Bristol Channel. 



Zoological considerations such as these require and imply the exist- 

 ence of parting barriers, even where no physical evidence whatever 

 of such may now remain. Geology in its future progress will be 

 called upon to define the positions and extent of many lines of partage. 

 The difficulty in the present instance is not great ; assuming such a 

 line we find the character of the accumulations on either side to be 

 as such conditions would require. On the French side, the quartz 

 shingle-beds at the base of the slate-series of Jersey, — the siliceous 

 conglomerate and sandstones of the Cotentin, mark the early existence 

 of coast-line in that direction. In this case palaeozoic sedimentary 

 strata are produced out of the abrasion of older portions of the same 

 great series, as the result of the elevation of deep-sea sediment (already 

 mineralized) to the sea-surface : and this change was progressive. 

 The Silurian series of the West of France presents at least two groups 

 separated by thick pebble-beds ; and this change is accompanied by 

 the transgressive passage of one series over the other, as in the "buttes 

 de Clecy." These lines affect east and west directions, from the 

 lowest ranges of the satiny and fibrous chloritic slate series upwards. 



On our side of the English Channel, the successive bands of shingle 

 subordinate to the Lower Silurian series of Cornwall equally require 

 the presence of a former coast-line, in somewhat close proximity there. 

 Attention was first called to the existence of rocks of this age in this 

 quarter by Prof. Sedgwick * . 



The direction of these bands indicates the relative position of the 

 coast, for I am disposed to consider the conglomerates of the Lizard 

 district to be of the same Silurian age. Guided by these considera- 

 tions, and their bearing on the direction which upraised older palaeo- 

 zoic beds assumed, we may feel assured that the lower or western 

 end of the Channel area was occupied by ridges or axes extending 

 eastwards. It is this line whose influence may he first traced in the 

 difference between the two Lower Silurian regions which have been 

 indicated above ; a divergence which becomes greater as the series 



* Quart. Journ. Geol. Soc. vol. viii. pp. 10, 11, &c. 



