Phj/sical Structure and older stratified Deposits of Devonshire. 667 



The same group on the north side of the Lizard serpentine also contains 

 calcareous beds ; not^ however^ passing into true beds of limestone; nor have 

 organic remains been yet found associated with it. Among its upper beds are 

 masses of coarse arenaceous rock, and beds of a very coarse red conglomerate ; 

 and south of Mawnan it contains a few very thin carbonaceous laminae*. 



Before our visit in 1836, Mr. De la Beche had completed his survey of the 

 north side of Cornwall, and laid down his results in admirable detail on the 

 sheets of the Ordnance mapf. These he kindly communicated to us; so that 

 in the few spots we visited to the south of Padstow, we only trod in his steps ; 

 on which account we avoid all details respecting this part of the north coast. 



The section from the slate rocks north of the Lizard to the cliffs north of 

 St. Ives Bay, appeared to us symmetrical. On both sides the killas is thrown 

 off by the granite; and among the slaty and arenaceous beds which appear 

 not far from Godrevey Island, are some cellular calcareous beds with ferru- 

 ginous bands containing obscure traces of organic remains. One of the larger 

 arenaceous masses reminded us of the Pennant stone of Bristol. We think we 

 may safely consider these beds as very nearly the equivalents of a part of the 

 group, north of the Lizard, which strikes into the coast near the mouth of the 

 Helford river. 



All the country round St. Agnes is so altered by the granite of Cligga point, 

 by injected Elvan dykes, and by innumerable metalliferous veins, that we 

 attempt not to define its exact geological relations — only remarking by the way, 

 that after the facts stated above, we have no right to place the more crystalline 

 slates of that district in any system lower than the groups above described. 



Before our examination of the north coast, Mr. De la Beche had collected 

 fossils from New Quay and other localities near the coast ; also on the Padstow 

 river, even so far up as the neighbourhood of Bodmin. We traced the cal- 

 careous slates with Encrinites, corals, and other fossils, through the cliffs north 

 of Mawgan Porth ; and the series is continued into Permizen Bay, west of 

 Padstow, where we had seen the calcareous slates with fossils during a former 

 visit to the county (1828). South of the Padstow river there are many irre- 

 gular contortions ; and the strike and dip undergo many changes, so that the 

 fossiliferous slates are spread over a wide surface. It is obviously (after what 

 we stated respecting the position of the beds south of St. Austell Moor) almost 

 impossible to find any transverse section that will clear up the relations of the 



* See Transactions of the Cambridge Philosophical Society, vol. i. p. 295. 

 t This map is not yet published ; but a reduced copy of it appears in the lately published Re- 

 port on the Geology of Devonshire and Cornwall. (1837.) 

 VOL. V. — SECOND SERIES. 4 R 



