English Stratified Rocks inferior to the Old Red Sandstone, 307 



Devon, would be to violate all the analogies of structure derived from 

 other parts of England ; and would not, the author believes, be sup- 

 ported by any specific evidence derived from fossils. 



CLASSIFICATION OF THE KOCKS OF CORNWALL. 



The author states, that the Plymouth limestone, in its range west- 

 wards, gradually thins off, and comes to an edge about the middle 

 of Whitesand bay. The strike of the beds and the trending of the 

 coast prevent this limestone and all the upper groups of the South 

 Devon section from appearing again on the south-eastern side of 

 Cornwall. 



The inferior portion of the first group (No. 1.) of the South Devon 

 section passes into Cornwall in a broad zone, gradually acquires the 

 strike of the Cornish rocks, and so runs along the S.E. coast; and 

 finallj'^ passes from Falmovith bay to Mounts bay ; rising on its north 

 side towards the granite, and on its south side dipping under the ser- 

 pentine of the Lizard district. As in Devonshire, the group contains 

 beds more or less calcareous, and, rarely, thin beds of limestone. 



In the same way, though not with the same clear evidence, the 

 calcareous slates rising from beneath the culm-measures near Laun- 

 ceston, double round the granitic promontory of Rough-Tor, and 

 are thence expanded (though with considerable irregularities of 

 strike and modifications of structure) as far as St. Ives' Bay, 



The granitic ridge of the county is supposed to represent an in- 

 terrupted mineral axis, on the N.E. and S.W. sides of which are 

 slaty groups of the same geological period. In all cases near the 

 granite the slaty groups change their structure ; but this change of 

 structure cannot be assumed as the ground of a classification depend- 

 ent on the age of the deposit ; as it is shown by a series of sections, 

 that in several places the fossiliferous slates on the coast are of the 

 same date with the indurated metalliferous slates that rise to the 

 granite. Hence the crystalline and metalliferous slates of Cornwall 

 are considered as metamorphic, and in that respect agree with the 

 bottom culm series that touches on the Dartmoor granite. 



Of the rocks of Cornwall the newest are the granites ; next come 

 the serpentine and other trappean rocks ; and the oldest are the slate 

 rocks. These slate rocks (including all the killas of Cornwall of 

 whatever structure) appear to be an actual prolongation of the lowest 

 group of the South Devon section, and therefore, agreeably to what 

 is stated above, are provisionally arranged near the upper portion of 

 the Lower Cambrian System. 



Many of these rocks were formerly considered primitive ; but none of 

 them have any pretension to that class. Numerous fossils were found 

 by the author in the cliffs on both sides Loe bay, and on both sides 

 of the Fowey river, and still further west in Gerrans bay. The Rev. 

 J. J. Conybeare found fossils many years since in the Tintagel slates ; 

 and the author in 1828 traced the fossiliferous system into the cliffs 

 west of Padstow. During M. De la Beche's survey he had (before 

 the author's last visit to the N.W. coast of Cornwall) found fossils 

 innumerable in that part of the county. The Cornish fossils are 



X2 



