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X. On the Geology of Devon and Corn^wall, *wit7i reference to 

 a paper read before the Geological Society on December ^th.^ 

 1839. By the llev. D. Williams, F.G.S. 

 To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 A S I do not consider the substance and spirit of my paper 

 on Devon and Cornwall, which was read at the meeting 

 of the Geological Society on the 4th inst. is fairly reported 

 in the Atheneeum of the 7th, I request you will favour me 

 with an opportunity of righting myself with your readers, and 

 of reporting progress since my communication which was 

 published in your last October Journal (vol. xv. p. 293). I feel 

 assured that I am not intentionally misrepresented in the Athe- 

 nseum ; the abstract however imputes to me (as I hastily read 

 it before I left London) that I hold mineral characters to be 

 everything and organic evidences nothing, in determining the 

 relative ages of strata. Now it was very distinctly read by the 

 Secretary, Mr. Darwin, that I did not consider the law pro- 

 posed by Dr. Smith to be of any value in classifying the 

 rocks of the earth in remote localities, if it did not suppose a 

 final and universal extinction of genera and species; and in 

 as much as some plants and animals would probably be en- 

 abled by the Creator to survive mutations which would be 

 death to others, I considered that a classification of the 

 older rocks should be regulated by some per-centage test, 

 such as Mr. Lyell had applied to the tertiaries, rather than 

 by a more restricted rule. I quote from memory, not being 

 able to refer to either the Athenaeum or to my paper. I stated 

 that I unequivocally believed in the extinction of genera and 

 species, severally at distant epochs, and therefore did not be- 

 lieve that the Posidonia and Goniatite, which I discovered in 

 some trashy lentiform limestones in Devonshire, were specially 

 created for the mountain limestone alone, when I knew it 

 could be proved to demonstration, that those Posidonia lime- 

 stones of Devon, and all their associated rocks, not only bore 

 no lithological resemblance to any of the mineral types of any 

 portion of the great English coal-field, but that they under- 

 laid the coral limestones of South Devon, and the whole of 

 the slates of Cornwall. I exhibited sections evidencing the ac- 

 tual supraposition of the Cornish killas on the floriferous 

 series. No. 9, and the Coddon grit. No. 8, and I pointed out 

 the localities. In all fairness then it remains for gentlemen 

 to disprove those facts, instead of requiring me to show what 

 I believe to be an impossibility, viz. the identity of the 

 plants I found in the great floriferous outlier on the south and 



