Sir E-. I. Murchison on the Silurian Rocks of Cornwall. 329 



with the Bellei'ophon trilobatus (Sil. Syst.) and the Loxomena 

 lincta (PhilHps). The first-mentioned of these shells is charac- 

 teristic of the tile-stones in Herefordshire and Shropshire^ and 

 is also found in strata of the same age in Cumberland (between 

 Kirby Lonsdale and Kendal), which form the uppermost band 

 of the Silurian rocks, or a transition from the Silurian into the 

 Devonian system. Now as Professor Sedgwick and myself had 

 inferred that the limestones of Looe and Fowey belonged to the 

 lower calcareous zone [of Devonshire, and as the sections of Sir 

 H. De la Beche show that the Polperro beds dip beneath the 

 Looe and Fowey rocks, the zoological evidences seem to harmo- 

 nize with recorded physical facts, and we thus obtain reasonable 

 grounds for believing, that the lowest Devonian and the upper- 

 most Silurian strata are exposed in the district which ranges 

 along the shores of that part of Cornwall, by Polperro, Pentuan, 

 &c. 



But if doubts should exist as to whether the Polperro slates 

 ought to be referred to the bottom of the Devonian or top of the 

 Silurian system, the discoveries of Mr. Peach in the headland of 

 the Dodman, and in the prolongation of its strata to Veryan Bay, 

 completely demonstrate, that still older and unquestionable Silu- 

 rian rocks are there present. This is the district in which both 

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

 ence of a line of elevation*, running from north-east to south- 

 west, which bringing up certain quartzose or argillaceous slates 

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

 the published section of the latter having clearly indicated these 

 relations. 



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

 by ]\Ir. J. Sowerby, are Orthis lata, O. orbicularis ^ another spe- 

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

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

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

 altei'nata of the Silurian system. The remainder are not, however, 

 referrible, as he had supposed, to Leptana lata, Terehratula nucula, 

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

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

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

 Orthis jiabellulum and O. testudinaria both belong, unquestion- 

 ably, to the Orthis [callactis B) t calligramma (Sil, Syst.), and 



* See Trans. Geol. Soc, n. s., vol. v. p. 666 ; and Report on Cornwall 

 and Devon, p. 84. 



\ This shell was called Orthis callactis B in the Sil. Syst. pi. 19, fig. 5, 

 but subsequent comparisons have shown that it is identical with the 0, cal- 

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



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



