Remarks on the " Devonian'''' System of Rocks. 355 



culm measures, and the slates of South Devon and Cornwall, 

 to be among the oldest transition 7'ocks. Still the first indi- 

 cations of a more accurate view, as given in his representa- 

 tion of the North Coast of Devon, is to us a strong proof both 

 of his boldness and sagacity. Doubtless deceived by mineral 

 characters, slaty cleavage, and the antique impress of many 

 parts of this region, he never thought of applying his own 

 sound principles to Devonshire, still less to the killas and so 

 called " primary " rocks of Cornwall. Yet is it entirely 

 thi'ough the application of Smith's " Strata identified by their 

 organic remains," that we have been enabled at length to 

 work out what we believe to be a correct classification of 

 these rocks, and to place them so much higher in the series 

 than had ever been contemplated by those who have gone 

 before us. The imbedded plants and shells, and the strong 

 analogy of the culm strata of Devonshire to those which we 

 had studied in Pembrokeshire, coupled with their overlying 

 position, first led us to venture to assert that so large a por- 

 tion of this region was truly an equivalent of our ordinary 

 coal fields : and assuming that our view has been sustainecl, 

 we have since shown, upon the same principles of imbedded 

 fossils and a conformable succession of strata, that all the 

 rocks which rise from beneath the great culm basin (with 

 perhaps some slight exceptions), whether slates, killas, lime- 

 stone or sandstone, form one great natural group (hitherto 

 called old red sandstone), which occupies the great interval 

 between the Carboniferous System above, and the Silurian 

 System below it; each of these thi'ee great systems being de- 

 fined, as we have before explained, by a characteristic series 

 of organic remains. 



We have much pleasure in stating that, since the appear- 

 ance of our memoir in the last Number of this Journal, the 

 reading of a paper by the Rev. D. Williams to the Geologi- 

 cal Society upon the structure of Devonshire, gave rise to a 

 discussion, during which certain explanations took place which 

 have happily removed from our minds any tendency to sup- 

 pose, that our fellow-labourers Mr. De la Beche and Mr. 

 Williams were unwilling to accord to us the merit (whatever 

 it may be) of having been the first to propose a great change 

 in the gi'ouping and classification of the rocks ot Devonshire 

 and Cornwall. We beg, therefore, to say, that Mr. De la 

 Bechc having in a kind and friendly manner read from his 

 Report the passagequoted below*,and having assured the geo- 



• " In 183G, Prof. Sedgwick and Mr. Murchison read a memoir before 

 the meeting of the British Association held that year at liristol, in which 

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