683 



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 whicli 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. Mr. 

 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 

 generally ill preserved ; but among them are some corals that are 

 common both to the Silurian and Cambrian systems. The fossils of 

 New Quay and South Petherwin are an exception to the remark ; as 

 many of them are well preserved. They consist of corals ; encri- 

 nites ; numerous specimens of the genera Terebratula, Oi'this, and Spi- 

 rifer; of iouv or five STpeciesoi Orthoceratites ; Goniatites ; and lastly, 

 three or four new species of a genus described by Count Munster 

 under the name Clymene, and by Mr. Ansted under the name En- 

 dosiphonites. As they occupy a position so much lower, so, as a 

 group, these fossils are distinct from those of the Silurian system. 



Conclusion. — The author here takes a retrospect of the preceding 

 description, and states that the classifications are founded on the 

 details of actual sections ; and that as far as such detailed sections 

 throw light on the several questions that may arise, there is not 

 much that remains to be done in England. Some of the generali- 

 zations are, however, founded on imperfect evidence ; and to render 

 them more complete, it is now necessary to appeal to the organic 

 remains in the several groups. In this department little has been 

 yet effected, excepting in the higher pavt of the Silurian system, 

 where the upper divisions (at least in one part of the island) assume 



