Vol. 65.] OVERTHRTTSTS AT TINTAGEL. 273 



The Tintagel Cliffs. 



Northwards of Lower Penhallic Point the cliffs are mainly of 

 Delabole Slates ; but the Woolgarden Phyllites (with ottrelite) 

 occur at the top, with patches of Barras Nose Beds near Lambs- 

 house Quarry and the Church. 



The volcanic rock is seen at Hole Beach ; it is cut off by a fault, 

 disappears for nearly a mile, and reappears on the foreshore about 

 a quarter of a mile south of Tintagel Island. At Trebarwith its 

 top is over 200 feet above the sea ; but the mass declines to the 

 north and disappears beneath the surface, then curving upwards and 

 reappearing near Gillow Quarry. An interesting fact, as proving 

 its underground extension, is that the lava was found 50 feet below 

 the sea in a borehole at Lambshouse Quarry, midway between Hole 

 Beach and Tintagel. 



Tintagel Island. 



It is difficult to describe the complicated geology of the Island, 

 but a good deal of it may be seen from the cliffs in front of Tintagel 

 Church. The steep southern cliff of the Island is crossed by bands 

 of rock of different colours representing difference of composition. 

 Two prominent blue-black bands are separated by a greenish zone ; 

 while silvery slate and phyllites both overlie and underlie these beds. 

 About half way along the southern cliff of the Island (fig. 5, p. 274), 

 these bands are interrupted near a cave, and a repetition of the 

 same rocks occurs. From the view (fig. 5) and from the section 

 fig. 3 (p. 270) the position of the bands will be seen. In order to 

 study them, it is necessary to follow the path leading to the Castle 

 gateway. At the bottom of the path are grey-green phyllites of 

 ill-defined characters, probably the Woolgarden Beds ; near the 

 bottom of the steps the Barras Nose Beds appear, covered by the 

 volcanic rocks. The steps, as far as their last bend to the right, 

 are cut in the volcanic rocks ; at the bend the Trambley Cove Beds 

 (Upper Blue-Black Slates) appear, and compose the cliff by the 

 Castle gateway. Just inside the gateway the Tredorn Phyllites 

 occur above the Trambley Cove Beds, but beyond the Castle wall 

 the lava is again seen. Nearly all the top of the Island is Tredorn 

 Phyllite. An other view of the two series of rocks in the eastern 

 cliff of the Island is seen from Tintagel Haven. If a descent is 

 made to the south side of the neck of land joining the Island to the 

 mainland, the first rocks to attract attention are the volcanics at 

 the base of the cliffs in front of the Keep. These are normally 

 overlain by the Trambley Cove Beds and the Tredorn Beds ; while 

 the Delabole Slates occur in the old quarries. Another prominent 

 feature is the great slickensided fault-face beneath the Keep, and 

 a little to the south are two smaller faults along which the sea 

 has worn caves. In these caves fine stalagmites and calcitic 

 encrustations may be seen. 



Immediately below the wall of the Keep the Barras Nose Beds 



