32 



THE GEOLOGICAL AGE OF CENTRAL AND WEST CORNWALL. 



The foUovring trilobites have been recorded, but are of doubtful occurrence : — 

 Calymene pulchella — recorded by Murchison, 1846. 



C Sternbergii — mentioned by Peach, 1844, doubted by Murchison, 1846. 

 C. Blumenbachii — mentioned by Murchison and Couch, but recorded by Salter. 



The pseudo-greenstones referred to above occur in several 

 places, the best-known locality being close to Terras Bridge, in 

 the parish of St. Stephens. This bed was analysed and described 

 by Mr. J. A. Phillips, in 1876, as probably an altered ash-bed, 

 or hardened hornblende slate. '^'' 



Some of the so-called greenstones of the Mount's Bay are also 

 merely altered slates, although others are undoubtedly intrusive 

 igneous rocks. 



The interstratified hornblendic schist and serpentine of Porth- 

 alla were mentioned in my paper on the Meneage peninsula 

 already referred to, and they are represented in the accompanying 

 section (Plate a). The strike of the whole series of beds in this 

 place is to the N.E., and they are all quite conformable with 

 each other — there being no indications whatever of intrusion so 

 far as I was able to see in three careful examinations. 



The S.W. strike is very regularly maintained by the rocks 

 which I have coloured as Lower Silurian on the accompanying 

 map. On the south side of the granitic chain they are very thick, 



* Quart. Journ. Geol. Soc. May 1876, pp. 175-178. 



