338 Sir R. I. IMurcliison on the Silurian Rocks of Cormvall. 



ments of a given epoch have been accumulated under pecuUar 

 conditions, we must expect to tind 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 

 pi'odigiously increased*." 



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

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

 when our works were published, seen any fossils from South 

 Cornwall sufficiently distinct to Avarrant 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 cpiestion, your associate ]\Ir. 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 IMeeting of the British Association, and concerning 

 which Professor Phillips and myself could only venture (so 

 obscure did they ajjpear to us) to give the guarded, though sug- 

 gestive opinion, which Mr. Peach has recorded in your thirtieth 

 Report. I then ventured to surmise, that these ichthyolites 

 might belong to the Upper Silurian rocks, the oldest in which 

 the remains of any vertebratcd animals had yet been discovered, 

 because " they occurred in rocks forming the axis of South Devon 

 and Cornwall, which I had always considered to be the oldest in 

 that country." 



In pursuing his researches, J\Ir. Peach published in 1844 a 

 sj'iiopsis of the Cornish fossils fnmi various localities, in which, 

 besides the ichthyolites of Polperro, he identified several mollusca 

 from Gorran Haven, Caerhayes, and Cam Gorran Bay, with 

 typical Silurian species. These were the fossils I was so anxious 

 to see at Penzance ; and Mr. Peach having obligingly forwarded 

 them to me in London, I no sooner unpacked the box, than I 

 found that true Silurian and even Lower Silurian rocks existed in 

 Cornwall, — the proofs being the presence of certain sim])le-plaited 

 Orthidce, which are invariably typical of that age. But although 

 jMr. Peach had come to a correct general conclusion, the specific 

 names he attached to the South Cornish fossils in your thirtieth 

 Reportare not correct. In respect to the ichthyolites from the slates 

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



