340 Sir R. I. Murchison on the Sihirian Rocks of Cornwall. 



Professor Sedgwick and Sir H. De la Beche had noted the exist- 

 ence of a Une of elevation*, running from north-cast to south- 

 west, which bringing up certain quartzosc or argillaceous slates 

 had thrown the beds otf, both to the south-east and north-west, 

 the pubhshed section of the latter having clearly indicated these 

 relations. 



The fossils found by Mr. Peach at Gerrans Bay, as determined 

 by J\Ir. J. Sowerby, are Or this lata, O. orbicularis, another spe- 

 cies resembling 6. plicata, and a fourth which does not appear 

 to have been published. At Caerhayes, Mr. Peach has collected 

 other forms of Orthidte, one of which approaches nearest to the O. 

 alternata of the Silurian system. The remainder are not, however, 

 referriblc, as he had supposed, to Lepta-na lata, Terehratula niicula, 

 Atrypa striatula, &c. The fossils from the Great Peraver quarries 

 in Gorrau Haven, on the eastern face of the Dodman, are still 

 more decisive ; for the species which Mr. Peach has named 

 Orthis flabellulum and O. testtulinaria both belong, unquestion- 

 ably, to the Orthis {callactis 'B)i calligramma (Sil. Syst.), and 

 witii it is a form undistinguishable i'rom the Orthis {canalis) 

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

 rock appears to mc to be the Cali/mene pulchella ? (Dalman) ; a 

 second species resembles C. Blumenbachii. 



No one accustomed to the Palrcozoic 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 jiortiou of 

 that system than the Orthis calligramma, which in Shropshire and 

 the adjacent ^Yelsh counties is found to range downwards, from 

 the vei-y 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 



* S?e Tians. Gcol. Soc, n. s., vol. v. p. CGG ; and Report on Coniwall 

 and Devon, p. SI. 



t This shell was called Orlliis cnlladk B in the Sil. Syst. pi. 19, fig. 5, 

 but subsequent comparisons have sliown that it is identical with the O. cal- 

 ligramma (Dalman) of Scandinavia, Ilussia, &c. 



In like manner, the Orlliis canalis of the Silurian system has proved to 

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

 oldest, are now nccci5sarily adopted. 



