Silurian Discussion. 113 



containing fossils, which lie between the Berwyns and Snowdon, 

 (the Cambria of Sedgwick), are the same as those I had drawn in 

 sections, and described in words, in the " Silurian System." 



If any one wishes to verify this statement, let him compare my 

 original coloured map and sections* of the country west of the 

 Longmynd (Stiper Stones and Shelve), with those detailed maps 

 and diagrams of the surveyors, which explain all the flexures and 

 breaks across North Wales, and he will then see that our hard- 

 working and able contemporaries have demonstrated that nearly 

 all the fossil-bearing strata of Cambria have their equivalents in 

 Siluria ; and that even the rocks of unfossiliferous greywacke, to 

 which Sir H. de la Beche and his followers now restrict the word 

 Cambrian, are more copious and thicker in the Longmynd of my 

 original tract of Shropshire, than in any of the similar North Welsh 

 masses which underlie the strata of Snowdon. This is not my 

 statement, but the deduction of the Government surveyors, after 

 many years of labour in the field. 



Supported as I am by such authorities, I can afford to be criti- 

 cised for two or three mistakes in a large work containing about 

 240 coloured sections, woodcuts, and views. Belying on the im- 

 partial judgment of numerous contemporaries, who know how 

 hard I laboured, and what I did effect in classification, I will not 

 dispute about a patch of Caradoc sandstone here, or one of Llan- 

 deilo flag there, since I have laid it down that these subdivisions 

 are characterised by many of the same fossils. The researches of 

 late years have, indeed, confirmed the unity of the Silurian System, 

 by shewing that many of the same species of fossils pervade the 

 vjhole series of its loiver and upper rocks. 



It is this fact which prevents the possibility of a change of 

 nomenclature, and the application of two unconnected names to 

 one system of life. In short, the proposed amputation of the lower 

 half of the Silurian System would, in my opinion, be a violation 

 of nature. 



In the work, Russia and the Ural Mountains, in which a general 

 view of the whole ascending order, from the lowest to the highest 

 strata, was given by my colleagues and myself, it was shewn that 

 the Silurian System, so thick in Britain, has in the north of Europe 

 so thin a vertical development (though equally divisible into very 

 rich fossiliferous lower and upper deposits) as to be quite incapable 

 of separation into two rock systems. But as Professor Sedgwick 

 does not like foreign parallels, I will conclude this letter by citing 

 two home geographical illustrations of the effect of his proposed 

 nomenclature. Let any one cast his eye over my map of the 



* u Silurian System," map, and pi. 31, fig. 4; pi. 32, figs. 1, 2, 3, &c. 

 VOL. LIU. NO. CV. — JULY 1852. 



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