1851.] SEDGWICK SLATE ROCKS OF DEVON AND CORNWALL. 13 



tions of these rocks. The quartzite of the Cam retains its usual struc- 

 ture, and contains fossils. Farther north, from under the rocks of the 

 Cam, rises a series of brownish ferruginous grits and coarse slates, 

 like those under the quartzite of Gerrans Bay ; and these grits at 

 Great Peraver also contain many fossils. 



A single day's excursion round the headlands above-noticed, com- 

 mencing at Truro and ending at St. Austell, and made during very 

 unpropitious weather, could not lead to the discovery of many fossils. 

 But in the Museums of Penzance and Truro we had seen a good 

 collection, made with great labour, chiefly by Mr. Peach, from the 

 rocks I have just noticed ; and I subjoin the following list, from 

 the species now deposited in those museums, with a reference to 

 the places where the several species were found. 

 From Great Peraver north of Gorran Haven : — 



Orthis elegantula, Balm. ; rare. 



parva, Pander ; very abundant. 



calligramma ? Dalm. 



turgida, M'Coy ; very abundant. 



flabellulum, Sow. ; very abundant. 



Caljmiene brevicapitata, PortlocJc. 



parvifrons ? Salter. 



Homalonotus bisulcatus, Salter, 



From the quartzite of the Great Cam : — 



Orthis testudinaria, Balm. ; abundant, 



■ retrorsistria, M'Coy ; abundant ; plentiful also in a 



part of the Bala group. 



Near Porth Caerhays ! — 



Orthis grandis ? Sowerhy ; a Bala species. 

 Cycloceras , a species like one in the Wrae Lime- 

 stone, Upper Tweed. 



All the above species (with the locality of each specimen carefully 

 recorded) are placed in the museum at Penzance, and were carefully 

 examined by Prof. M*Coy, kindly assisted by Mr. Crouch, the 

 Honorary Secretary of the Cornish Geological Society ; and, with a 

 like kind assistance from Dr. Barham and Mr. Whitley, we found 

 several duplicate specimens of the same species, and frem the same 

 localities, in the museum at Truro. Specific names were not affixed 

 to many of the specimens, and for the previous list I rest entirely on 

 the authority of Prof. M'Coy. 



From the above list (I believe in near accordance with one lately 

 given by Sir B. I. Murchison*), it is obvious that a large group of beds 

 with fossils of the Cambrian (Lower Silurian) age exists along the 

 line of coast above described. But from the previous descriptions, 

 and from Mr. Whitley's section, fig. 1, the group appears to overlie 

 the calcareous slates of Veryan, which we suppose to be Devonian. 

 In hke manner, if we examine the coast-section from the head of St. 

 Austell Bay to the Dodman, we find the fossiliferous group between 

 Peraver and Gorran Haven in what appears to be a high part of the 

 * Trans. R. Geol. Soc. Cornwall, loc. cit. p. 321. 



