Silurian Discussion. 119 



deilo flag — is, by this new scheme of development, identical in age 

 with beds at least 25,000 feet in thickness, which undulate 

 between the Berwyns and the Menai ! And a monstrous develop- 

 ment is to be followed by a new and monstrous nomenclature, in 

 which a great fundamental group which does not exist in Wales 

 is to be called Cambrian, while the grand series of the older Cam- 

 brian rocks are to be called Silurian, though they form the moun- 

 tains of Wales, and do not exist at all in the typical Silurian re- 

 gion. No authority, however great, can perpetuate such an incon- 

 gruous and unwarranted nomenclature ; and it is historically as 

 unjust as geographically it is incongruous. 



From the very first, the term Silurian System was used prema- 

 turely by its author, and against repeated remonstrances on my 

 own part. For the system had no clear physical or zoological 

 base. Many of the fossils found below it in the Cambrian rocks, 

 I affirmed to be of the same species with those in the two lower so- 

 called Silurian groups. Advancing knowledge strengthened these 

 objections, and it was at length discovered that the whole system, 

 according to the author's scheme, rested physically on a false base. 

 But there is still a good Silurian system, agreeably to my friend's 

 use of the word System, based on the Caradoc sandstone. This 

 sandstone is a great mechanical and often an unconformable de- 

 posit, constituting the true connecting links between Cambria and 

 Siluria. It partakes of the zoological characters of both regions. 

 At May Hill its fossils seem to be those of the Wenlock stage. At 

 Horderley they very nearly approach to those of the Bala stage. 

 Is there any single Caradoc section where these two fossil groups 

 appear together ? If so, are the types blended or superimposed % 

 Some questions of this kind require a careful re- examination ; 

 though they have already been excellently handled by Professor 

 Phillips. If questions such as these were completely solved, we 

 should, I think, need nothing more for a full history of the true 

 sequence and natural progressive development of the oldest fossil- 

 bearing rocks of Britain, beginning with the Cambrian and ending 

 with the Silurian series. 



To the concluding words of my friend's comment (Literary 

 Gazette, April 24, p. 370), I express my heartfelt concurrence. 

 When we went round the Highlands of Scotland in 1827, I was 

 then his superior in physical endurance ; but a quarter of a cen- 

 tury has, alas ! made me but a sorry labourer in the field. Still 

 I am not without hopes of again meeting him in his true Silurian 

 country, and endeavouring to settle, along with him, one or two 

 minute, and not laborious, questions of demarcation to which I 

 have just pointed. 



Adam Sedgwick. 



