272 ME. H. DBWEYON [Aug. 1909, 



of the beds at the surface is due to the north-westerly hade of the 

 thrust-planes. As shown on the map (PI. XIII), the great anticline 

 in which the beds of the normal sequence are folded pitches north- 

 westwards, and produces a similar effect to that produced by the 

 hade of the thrust-planes (T 1 & T 2 ) in bringing to the surface the 

 lower beds towards the south-east of the area shown in the map. 



IV. The Coast-Sections. 

 Trebarwith Valley and Cliffs. 



Trebarwith Strand, in the southern part of the map, is a popular 

 resort, and is easily reached by a road from Camelford Station. 

 This road is called the Sanding Road, and between the station and 

 the sea it crosses all the rock-types dealt with in the present paper, 

 following a valley in which excellent sections are exposed. On the 

 east the basset-edges and crags are composed of Delabole Slate and 

 its varieties. This slate was quarried at the numerous great 

 quarries on each side of the road, and these supply fine material 

 for study of the rock. Near Trewarmett Bridge the Woolgarden 

 Phyllites appear, and extend westwards for some distance, at first 

 interfolded with the Delabole Slate, but afterwards alone. By 

 the lane leading to Trebarwith Village the Barras Nose Beds 

 are seen ; and in the lane north of the valley, running between the 

 Mill and Tintagel, the slaty rock was quarried. Beyond this place 

 the picturesque craggy rocks of Treknow Valley belong to the 

 Volcanic Series. 



Above these beds the Trambley Cove and Tredorn Beds are found. 

 It is difficult to describe exactly their distribution; but, in general, 

 it may be explained that the tops of the hills and cliffs between 

 Treknow Valley and the sea are composed of Tredorn Phyllites. 

 The same phyllites also occur on the top of Dennis Point and run 

 down to Treligga. Below them lie the blue- black slates (Trambley 

 Cove Beds), which are also exposed in the lane leading from 

 Trebarwith Strand to Treknow, and in Port William Bay by the 

 roadside and on the foreshore. 



Over this area the beds dip to the west by south, so that they 

 appear both inland and in the cliff-face. In walking along Tre- 

 barwith Strand the cliff-face can be studied, and the volcanic rocks 

 which constitute the foreshore are seen in the cliff-face covered by 

 the Trambley Cove Beds, while the Tredorn Beds compose the cliff- 

 top. The succession continues as far as Lanterdan, where the over- 

 thrust Delabole Slates occur as seen in fig. 2 (p. 268J and described 

 on p. 269. Concentric bands of vesicles filled with calcite reveal 

 the pillow-forms in the volcanic rocks at Trebarwith Strand, and at 

 Vean Hole several shear-lenticles appear at the top of the Trambley 

 Cove Beds. Penhallic Point is the best place to view the whole 

 cliff-range, and from here the marked change caused by the differing 

 hardness of the beds is pronounced. 



