1868.] IIOLL SOUTH DEVON AND EAST COKNWALL. 423 



four miles would imply a great accession of deposits unrepresented 

 elsewhere. On the west these slate- and ash-beds appear to rise up 

 over lower rocks ; but on the east their relation to the argillaceous 

 slates about Pillaton is not quite so clear, as the nearly W.S.W. 

 fault from Pentre Cross may be prolonged across the Notter at 

 Pillaton Mill, and, if so, would not be without its influence on the 

 rocks of the Tiddi valley. 



Assuming that the volcanic rocks of St. Clear, New Bridge (on the 

 Notter), Callington, Hay, South Hill, and Bray's Shop belong, as 1 

 believe, to the same geological horizon as the long belt which, bor- 

 dering the granite on the north, runs up by j^orth Hill to the south 

 of Alternan, the beds which dip into the synclinal area of Liskeard, 

 and undulate thence to Saltash and St. Stephens, represent in less 

 force the higher group of Davidstow and Lewannick. Folded in 

 among tliis upper group are some slate-beds locally fossiliferous, as 

 at the Tregril slate-quarry, at Great Tressell north of St. Keync, 

 Doublcboys, Stoney Bridge, near Liskeard, and in the cuttings of 

 the railway south of the town, and likewise at Saltash and St. 

 Stephens. Among these fossils we find noticed Pleurodictyum jpro- 

 hlematicum, Atry^a desquamata, Bellerophon bisulcatus, FenesteUa 

 antiqua, an Orthoceras, two species of Sjnrifera, some undetermined 

 CyatliophyUklce, Phacops latifrons, and P. punctatus. The last 

 species was found at Great Tressell by Mr. Pengelly, and is a cha- 

 racteristic Middle-Devonian fossil *. 



South of St. Stephens the slates and ash-beds dip to the south. 

 They include some calcareous bands, and pass under a thick series 

 of argillaceous rocks of grey, blue, and purple colours, interstra- 

 tified with ash-beds, which lead up to the base of the Plymouth 

 limestone. These beds are laminated at a high angle, and appa- 

 rently the lamination is in the plane of the bedding. East of the 

 Hamoaze the beds seem to form a short synclinal trough, the slates, 

 which are vertical along a line extending from Tor Point to Anthony, 

 dipping northerly at high angles along the shore of Sango Lake. 

 They are, however, again thrown over to the south at Wolsden 

 House, and become undulated and contorted at St. John's, but again 

 dip southerly at Mendinnick, and this dip is preserved all the way 

 to the Rame Head, the slates south of Higher Tregantle being more 

 or less hard and arenaceous, with uneven surfaces, and often inter- 

 stratified with grit bands. At Wolsden House these contorted beds 

 contain some calcareous seams, and a bed of volcanic ash occurs to 

 the south of the park ; a few grit bands may be seen between the 

 village and Mendinnick, but the contortions which may be here 

 observed die out before reaching the coast. The slates of Tor Point, 

 which are there chiefly grey or blue, range past Anthony to Graft- 

 hole, where they become reddened and include thin bands of grit. 

 If we recross the beds from the coast at Port Winkle to the lime- 

 stone of St. Germans, which is on the same line of strike as the cal- 

 careous bands south of St. Stephens, we find that the variegated 



* Fig. in Palaontograpliical Society's Monograph on Trilobites, vol. i. part 1, 

 by Mr. Salter, pi. 1. figs. 17-10. 



