oj Silurian Bocks in Cornwall. 35 



conditions, wo 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 tlieir hard and slaty charac- 

 ter; and under such circumstances, the difficulty of precisely li- 

 miting the boundary line of any portion of them is prodigiously in- 

 creased."* 



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

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

 our works were published, seen any fossils from South Cornwall suf- 

 ficiently 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, be- 

 lieved (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 expansions of the fossiliferous " Devonian" 

 strata. In this state of the question, your associate Mr Peach be- 

 oran his labours in collectinor fossils alonor 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 ex- 

 hibited at the Cork Meeting of the British Association, and concern- 

 ing which Professor Phillips and myself could only venture (so ob- 

 scure did they appear to us) to give the guarded, though suggestive 

 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 verte- 

 brated 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.'^ 



lu pursuing his researches, Mr Peach published, in 1844, a sy- 

 nopsis of the Cornish fossils from various localities, in which, besides 

 the ichthyolites of Polperro, he identified several mollusca from Gor- 

 ran Haven, Caerhayes, and Carn Gorran Bay, with typical Silurian 

 species. Tlieso 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 

 oven Lower Silurian rocks existed in Cornwall, — the proofs being 

 the presence of certain simple-plaited Orthid/e, which are invariably 

 typical of that age. But although Mr Peach had come to a correct 

 general conclusion, the specific names he attached to the South Cor- 

 nish fossils in your thirtieth Report are not correct. In respect to 

 the ichthyolites from the slates of Polperro, Pcntuan, &e., they have 

 been referred to our mutual friend Sir Philip Egerton, who his bet- 

 ter versed in the classification of Agassiz than any of our countrymen, 

 and he thus writes to mo concerninor them : — " These remains are 



o 



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



