1868.] nOLL SOUTH DEVON and east CORNWALL. 425 



ward of tho Looe river is not unattended with difficulty. It ha^ 

 been already stated that a fault extends from the west of Bodmin, 

 by Lostwithiel, towards the coast. A second fault trends from the 

 mining-district of Pembroke across the Gribbin promontory to 

 Combe Hawne, near the mouth of the Fowey. This latter fault 

 has thrown up the country on the north, and brought up at Pcn- 

 carra Head, Powey, and Tywardreath the rocks which passed down 

 at Tredinick, Tremain, and St. Veep, forming a synclinal trough 

 which contains the fossiliferous rocks of the Looe river, together 

 with some red and variegated argillaceous beds which range up 

 from the coast at Talland, by the north of Lansalloes and Oregon, 

 across the Powey, towards Tywardreath. These red slates appear 

 to be a continuation of those which, trending down from Polbathick, 

 become partially reddened at Narkurs and Treliddon, and reach the 

 coast at the mouth of the Seaton river ; and if the upcast of the 

 coast -line between Talland Bay and Gibbin Head is not entirely 

 due to the fiiult already noticed, but is partly owing to an anticlinal 

 axis out at sea, south of Polperro, it is not impossible that such axis 

 may curve round, parallel with the belt of variegated slates, and 

 strike the coast of Whitesand Bay at St. Germans Beacon, accom- 

 panied by inversion of the strata, and terminate in the bed of the 

 Lyhner north of Anthony. In that case, the grits of Sheviock Wood 

 would be the same as those of Carracawn Cross, with the slates of 

 Polbathick folded in between them. 



Notwithstanding the apparent contrariety of the dips, and the 

 consequent difficulty of obtaining satisfactory evidence, I believe 

 that the argillaceous rocks of Lanreath and the north of St. Veep 

 rise up from beneath the fossiliferous and purple slates on the south, 

 and overlie the gritty beds of Boconock. Looking to the general 

 structure of the country, and to the manner in which the slates 

 with ash-beds of Saltash and St. Germans are carried north-west- 

 ward by Liskeard and St. IS'eots, rising up over lower rocks on 

 the one hand, while the calcareous and argillaceous rocks that over- 

 lie them are curved southward across the Looe river to the 

 mouth of the Powey on the other, it appears more consistent with 

 probability that the grits and thick slates associated with them are 

 lower rocks broadly elevated rather than higher beds troughed in a 

 shallow basin. In mineral character they resemble those of the 

 Bodmin district, and appear to be the same disturbed in their line 

 of strike by the Lostwithiel fault, and have no resemblance petro- 

 logically to the higher rocks of the Plymouth country. Moreover 

 the slates of the mouth of the Powey, and of the coast thence to 

 Polperro, which support the red rocks on the north, contain Pterasj)is 

 Cornuhicus, M'Coy, which has been found also in the slates of Cliff 

 on the Powey, and in the vicinity of St. Yeep ; it occurs likewise 

 on the same line of strike in the calcareous slaty rocks at Milladon, 

 near St. Germans*. 



The fossiliferous slates of Saltash and St. Germans, with their in- 

 cluded volcanic ash-beds, brought down from the north-west by 

 * For a different interpretation, see De la Beclie, Kep. pp. 80, 81. 



