Sir R. I. Murchisou on the Silurian Rocks of CormcaU. 341 



group : they probably represent the upper portion only of the 

 Caradoc sandstone ; for the Orthis canalis, or elegantida, and the 

 Cahjmene lyulchella'^ (Dalm.), closely allied to C. Blumenhachii, 

 are AVcnlock, as w^ell as Caradoc, fossils. Judging from the fos- 

 sils only, I should say that the beds at Gerrans Bay with the 

 Orthis orbicularis are younger than those of Peraver and Gorran 

 Haven. Time and careful researches will, however, determine 

 this question of detail, and all I can now express is my opinion, 

 that the quartzose rocks and killas which extend from the tracts 

 above alluded to, to the mouth and centre of the bay and harbour 

 of Falmouth (probably much fm-ther to the south-west), are of 

 Silurian age also. 



The energy of Mr. Peach having thus afforded us the key by 

 which new lights are thrown upon the succession of Cornish 

 strata, 1 cannot but hope that, when the government geological 

 surveyors revisit Cornwall, they will define the exact demarca- 

 tions between these Silurian masses and their overlying Devonian 

 neighbours. In fact, I have within these few days been talking 

 over this subject with my friend the Director-General of the Sur- 

 vey, and he has pointed out to me on his detailed map, how, 

 from the enormous flexures which the strata have undergone in 

 their range from Devon into Cornwall, it is highly probable that 

 Silurian rocks (the equivalents of those alluded to) may be re- 

 cognised in other parts of Cornwall. Thus, the quartzose rocks 

 of Pydar Down or IMoor, to the north of St. Columb, which form 

 an east and west axis, dipping to the north and south under fossili- 

 ferous Devonian strata, may (he thinks) prove to be also of Si- 

 lurian age. But, forbearing to s])eculate on the probable results 

 of future researches, it is my decided belief, that the slaty rocks 

 constituting the great southern headland of Devonshire, at least 

 all the schists, &c. to the north of the Start Point, will eventually 

 be classed with the Silurian group of South Cornwall; for if the 

 Plymouth group of limestones, so prolific in animal remains, 

 afforded us the means of deciphering the age of less clearly de- 

 veloped zones on the same horizon in Cornwall, the Silurian 

 types collected by J\Ir. Peach may enable us to carry out a more 

 correct classification in still older strata, from Cornwall into the 

 obscure southernmost promontory of Devonshire. In the mean 

 time, confining ourselves to what we now know, it is manifest 

 that Cornwall exhibits in asceiuling order from north to south, — 

 1st, a band of true Silurian rocks; Snd, a zone of intermediate 

 character, forming a transition between the Silurian and Devo- 

 nian systems ; 3rd, a copious Devonian system, characterized by 



* The Calijmcne jmlilicUa (Dalni.) occurs botli in tlio inferior part of tlio 

 Upper Silurian, and the higiicr part of the Lower Silurian, in Swcilcn, Silu- 

 ria and Wales. 



