Sir R. I. Murchison on the Silurian Rocks of Cornwall, 327 



Phillips* ; who, in pointing out in certain tracts the connexion 

 of this group with the carboniferous fossils, which he had so well 

 described, and in others with the Silurian forms I had published, 

 had also concluded that the great mass of fossiliferous strata 

 which rise up from beneath the culm measures of central Devon 

 were of the same intermediate characters. In his valuable Maps 

 of Cornwall and Devon, Sir H. De la Beche gave essentially the 

 same views of geological succession ; and lastly, in his Report 

 upon the geological structure of that region, he described certain 

 detailed sections in the southern districts of Cornwall, to which 

 I will presently advert. 



In proposing the word " Devonian,^^ as applied to the inter- 

 mediate strata in question. Professor Sedgwick and myself for- 

 tunately thus qualified our meaning in regard to the extension 

 of such rocks into Cornwall : — '^ In asserting that the stratified 

 rocks of Devonshire and Cornwall are, upon a broad scale, the 

 equivalents of the Carboniferous and Old Red systems, we do not 

 however deny, that in certain tracts the lowest members of some 

 of these rocks may represent the upper division of the Silurian 

 system ; for although we have as yet found few if any of the 

 fossils most typical of that system, we admit that when the sedi- 

 ments of a given epoch have been accumulated under peculiar 

 conditions, we must expect to find considerable variations in the 

 forms of animal life. Again, we know that the rocks of this 

 region have undergone great changes in assuming their hard 

 and slaty character ; and under such circumstances, the difficulty 

 of precisely limiting the boundary line of any portion of them is 

 prodigiously increased f/^ 



The truth is, that neither Sir H. De la Beche and Professor 

 PhiUips, nor Professor Sedgwick and myself, had, at the time 

 when our works were published, seen any fossils from South 

 Cornwall sufficiently distinct to warrant the conclusion, that it 

 contained forms of an older type than those which had been 

 detected in North and South Devon and in the west of Cornwall. 

 It was therefore believed (and all geological maps were coloured 

 accordingly) that the zone of rocks occupying the southern 

 headlands of Cornwall, between the Bay of Plymouth on the east 

 and the Lizard Head on the west, were simply downward expan- 

 sions of the fossiliferous " Devonian '^ strata. In this state of 

 the question, your associate Mr. Peach began his labours in col- 

 lecting fossils along the southern headlands of Cornwall. He 

 first ascertained that certain forms first discovered by Messrs. 

 Couch in the environs of Polperro were fishes, which he exhibited 

 at the Cork Meeting of the British Association, and concerning 



* Pala?ozoic Fossils of Devon and Cornwall, 

 t Phil. Mag. 1839, vol. xiv. p. 241. 



