Vol. 65.] OVEBTHEUSTS AT TINTAGEL. 271 



capping at the top of the cliff, and that as the cliff descends to the 

 sea the underlying Woolgarden Phyllites reappear in its face, 

 followed by the Delabole Slates, which compose the rest of the 

 cliff to below sea-level. That is to say, one meets with a repe- 

 tition of the beds on walking from east to west, with lower beds 

 lying above the higher. This disposition of the beds could only 

 have been brought about by overthrusting (T t ). 



Folding would have caused the beds to crop out in either of the 

 following orders : — Beds 4, 3, 2, 1, 2, 3, 4, in the case of an 

 anticline ; or Beds 1,2, 3, 4, 3, 2, 1 in the case of a syncline. 

 The repetition shown in the section is Beds 1, 2, 3, 4, 5, 6, 1, 

 2, 3, an order of succession which could only have resulted from 

 overthrusting. South of this section the higher beds are not found ; 

 but, as seen in the next section (fig. 3, p. 270), the higher beds 

 of the series appear at Tintagel. In this section the sequence 

 is again normal as far east as the Castle Keep ; but the beds are 

 folded into a syncline and anticline. At the Keep a repetition of 

 the lower beds commences, and we find the Woolgarden Phyllites 

 and the Barras Nose Beds overlying the upper beds of the series. 

 The section also shows the volcanic rock at the base of the cliff 

 below the Keep, and the higher members of the series in the cliff- 

 face. The left side of the section shows the structure of Tintagel 

 Island (see also fig. 5, p. 274). On the south-eastern coast of the 

 Island all the beds of the series are seen in the cliff-face, and the 

 lower beds can be easily recognized as the continuation of the lower 

 beds at the Castle Keep : that is, they form part of the overthrust 

 mass (T x ). The section, however, shows a second repetition of the 

 beds, about half way along the southern cliff of the Island. These 

 beds, although inaccessible in the cliff, are recognizable by their 

 colours from a distance, and some of the beds can be examined 

 on the Island (see p. 273). There is, consequently, evidence of 

 two overthrust masses ; and, for simplicity, these will be lettered 

 A and B. 



Turning to the fourth section (fig. 4, p. 270), the normal sequence 

 is again seen on the east, succeeded by (ii) the Woolgarden Phyl- 

 lites, (iii) the Barras Nose Beds, and (iv) the volcanic rocks of the 

 overthrust mass, A. At Barras Nose (see fig. 6, p. 276) , the second 

 overthrust mass, B, is admirably exposed (see p. 275). Here again 

 the argument applied to account for the first repetition of beds holds 

 good ; namely, that the second repetition is due to overthrusting. 



These four sections are drawn approximately at right angles 

 to the strike of the beds, and fail to bring out the hade of the 

 thrust-planes. This is indicated on the map, where it will be 

 observed that on the south, only the lowest bed of the overthrust 

 mass is found ; but, as we proceed northwards, the higher beds of 

 the series come to the surface. Thus, at Lanterdan Quarry, only 

 the lowest bed is found ; at Dria Quarry the Woolgarden Phyllites, 

 and at Lambshouse Quarry the Barras Nose Beds are exposed ; while 

 at Tintagel all the beds occur. It is obvious that this disposition 



