330 Sir R. I. Murchison on the Silurian Rocks of Cornwall. 



with it is a form imdistinguishable from the Orthis (canalis) 

 elegantula (Sil. Syst.). The only well-preserved trilobite in this 

 rock appears to me to be the Calymene pulchella ? (Dalman) ; a 

 second species resembles C. Blumenbachii, 



No one accustomed to the Palseozoic rocks can throw his eye 

 over the fossils from these three localities, without at once recog- 

 nising them as true Silurian types. They have an entirely di- 

 stinct fades from the fossils of the overlying Devonian system, 

 and none of the species so abundant in North-western Cornwall 

 are here present. With my imperfect knowledge of the country, 

 it would be premature to say that subdivisions can be established 

 in this highly dislocated region, so as to define Upper and Lower 

 Silurian bands. But it may safely be asserted, that the fossils 

 of Gorran Haven are Lower Silurian types ; there being no one 

 species more eminently characteristic of the inferior portion of 

 that system than the Orthis calligramma, which in Shropshire and 

 the adjacent Welsh counties is found to range downwards, from 

 the very uppermost beds of the Caradoc sandstone into the heart 

 of the Snowdon slates, and is equally typical of the Lower Silurian 

 rocks of Russia and Scandinavia. At the same time, I do not 

 think that the Gorran Haven beds lie deep in the Lower Silurian 

 group : they probably represent the upper portion only of the 

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

 Calymene pulchella^ (Dalm.), closely allied to 6\ Blumenbachii, 

 are Wenlock, as well 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 further 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, 



be the O. eleganhda of Dalman ; and the names of that author being the 

 oldest, are now necessarily adopted. 



* The Calymene pulchella (Dalm.) occurs both in the inferior part of the 

 Upper Silurian, and the higher part of the Lower Silurian, in Sweden, Silu- 

 ria and Wales. 



