1868. J IIOLL SOUTU DEVON AND EAaT CORNWALL. 410 



The two masses of volcanic rock on either side of the Inny at 

 Trccarrel liridge appear to be portions of the same band, troughing 

 some of the higher beds between them, as already noticed. A 

 tolerably good section is seen in the lane leading from the bridge to 

 Tregvis, the volcanic rocks rising as an arch, which throws off a 

 thin covering of the higher slates ; on the south these undulate for 

 about a hundred yards, when the volcanic rock again rises, overlain 

 by the slates. A little further on, these rocks are overlapped by the 

 Cidm-measures. 



The belt of slates in which the volcanic rocks we have been con- 

 sidering are included is readily followed westward from 8t. Clether, 

 byDavidstow and Lesnewth, to the coast at Trevalga, where they curve 

 south-west to Tintagell, and are there associated with slates that 

 contain Pett-aia Celtica, Phacops latifrons, Stroijlialosia productoides, 

 Spirifera disjuncta, and its varieties (jiyantea and inornata, lihyn- 

 chonella pleurodon, Pterinea subradiata, and Splrlfera speciosa, all 

 of which, with the exception of the last two, are also met with at 

 South Petherwin. The greenish-grey slaty rocks which support 

 the volcanic belt of Tregue Cross and Penhale dip under it, and 

 strike, by Trevillan's and St. Kitt's, round the north-westward of 

 Cadon Earrow, lower rocks containing some thin grits being brought 

 up south-eastward of the barrow, and about Camelford. To the 

 westward of these lower rocks, and overlying them, there is a belt 

 of similar greyish slates striking up from below the volcanic beds of 

 Tregreenwell, east of St. Teath to Delabole, where the rock has 

 long been worked for roofing- slates, and thence to the Trewaruet 

 slate -quarries, where it curves round to the coast at Tregatta. 

 The exact mode in which this range of slates is brought into con- 

 tact with the higher rocks of Tintagell is somewhat obscure ; but the 

 abrupt change in the direction of the strike suggests the probability 

 of a fault crossing the country somewhere betwen Tregatta and 

 Tintagell. The dip of the Delabole and Tregatta belt of roofing- 

 slates is to the west, south-west, and south, as they curve round to 

 the coast ; and if they are, as they appear to be, the same as those 

 which support the volcanic rocks of Tregue Cross and Penhale, the 

 higher beds of Delamear Down (under which these slates dip) must 

 be the same as those of Davidston and St. Clether, but without the 

 interstratified bands of igneous rock. These latter, however, again 

 come in soutli of St. Teath, where the beds begin to widen out to form 

 a broad shallow trough with minor axes ; and as this trough trends 

 round to the westward, it deepens, and includes higher beds, some of 

 which are calcareous and correspond in geological position with the 

 fossiliferous beds of South Petherwin. The slates which include these 

 ash- and lava-beds, and support the higher rocks troughed in the syn- 

 clinal axis, form therefore two belts : — a northern, which trends east 

 and west from the south of St. Teath, atTreburget, to Pentire Point; 

 and a southern, which is continued by St. Tudy and St. Mabyn, and 

 then curves round to the Camel river at Egloshayle, beyond which it is 

 continued without the volcanic bands, by the south of St. Breock and 

 St. Ervan, to the coast at Bedruthcn. Some of these volcanic bands 



