180 THE GEOLOGIC^ili AGE OF CENTRAL AND WEST CORNWALL. 



beds is not less than 4000 feet. The Looe and Polperro beds 

 liavino- been already shewn to be Loivest Leconiiui there is, we 

 think, in this 4000 feet of rock plentj^ of room for the time which 

 elapsed between the Ludloiv and the Lotoer Dci:onian, and therefore 

 the Fowey beds may very well be Upiyer Silurian. That this was 

 the opinion of both Peach and Couch we have already stated 

 (v. supra pp. 166-7), and we have been glad to find that our 

 opinions, formed independently, have been so exactly confirmed 

 by what these able local authorities had previously published 

 on the subject. We believe, in fine, that those writers who have 

 so hastily and positively asserted that the whole of these rocks 

 are Devonian have either not studied the literature of the 

 subject, or have not attached sufiicient weight to the opinions of 

 the local geologists quoted above, whose experience rendered 

 their judgment most valuable. 



Lower Silurian. 



As to the topographical extension of these rocks so far as 

 they have yet been determined, we have little to add to the 

 former paper. We have indeed, in company with Mr. Clark, 

 traced them as we believe to the eastward about a mile beyond 

 Lostwithiel ; but, except this, have made no alteration in the 

 bouudaries formerly indicated. The fossiliferous beds of the 

 series are for the most part quartzytes, they have been traced 

 from Grorran to Bojorrow in Meneage — a distance along the 

 strike of some 25 miles. 



The Geological Rorizon of the Quartzytes. These have been 

 usually considered as the equivalents of the Caradoc Sandstone, 

 but the fossil evidence seems to us to shew that they are 

 somewhat older. The only fossils which can be said to have 

 been adequately studied are the trilobites — 10 species — worked 

 out by Mr. Salter in the years 1862-1867, and the brachiopods — 

 6 species — similarly worked out by Mr. Davidson, ia 1879-80. 

 The fossils of the underlying limestones, and the other fossils of 

 the Quartzytes themselves can scarcely be said to have been, as 

 yet, sufficiently determined to be of service in this particular 

 enquiry. The following are the fossils referred to ; — 



