Yol. 59.] THE TINTAGEL AND DAVIDSTOW DISTRICT. 409 



great importance. First!}', from St. Clether on the east to the Rocky 

 Valley on the west, the regularity of the strike which trends east- 

 south-eastward and west-north-westward is the most conspicuous 

 stratigraphical feature ; and secondly, that — more or less out of their 

 position as determined by the above-given strike — all the higher 

 beds come in along the coast from the Rocky Valley to Trebarwith 

 Strand, the most southerly point touched. This arrangement 

 appears due partly to a change in dip from a northerly to a 

 westerly direction — producing a kind of hemidome ; and partly to 

 north-north-easterly faults. 



The geological structure is reflected by the aspect of the country. 

 Thus, looking inland from some point on the cliffs between 

 Trebarwith Strand and Trevena, we see a plain, consisting of 

 the higher beds, greatly disturbed, rising almost inappreciably 

 to the east as far as a north-and-south line joining Trenale, 

 Downrow, and Trebarwith. 



Abruptly beyond this line rise the hills on which lie Trenalebury 

 Camp and Meneden, consisting of beds having the normal east- 

 south-easterly and west-north-westerly disposition. The plain is 

 broken to the north by the Rocky Valley, northward of which again 

 the ground slopes with a gradually-falling profile from Tregatherel 

 to Trambley Cove and the Saddle Rocks. 



Along this strip of country the orderly sequence of beds is pre- 

 served, and the east- south-easterly and west-north-westerly strike 

 continued to sea-level ; but on the south, as above remarked, where 

 the hills rise from the flat coast, a region of extensive faulting 

 appears to separate the folded beds near the sea from those of more 

 regular disposition to the eastward. 



The mineralogical composition of the beds may be responsible 

 for the not uncommon absence of conspicuous effects of pressure. 

 Taken as a whole, the greater mass consists of comparatively-soft 

 sedimentary rocks, usually built up of closely-matted flakes of white 

 mica, and resembling the phyllites of the Ardennes. On one horizon 

 they are banded (as, for example, at Hallwell Cottage, Benoath 

 Cove, Trewassa), and here the bands commonly are not contorted. 

 Although a reconstruction of the original sediment l on the whole 

 must have preceded pressure, examination of thin sections does not 

 invariably show clear evidence of such a sequence, probably, in 

 many instances, owing to a later mineral reconstruction which has 

 masked the effects of pressure. This is also usually true of the 

 Volcanic Series. When, however, we examine the Blue-Black Slates 

 overlying the Volcanic Series we generally find, not only intense 

 contortion in the more finely-banded members, but that occasionally 

 crushing has been sufficient to reduce the rock to the condition of a 

 fault-breccia. 



The cliffs to the south of Trambley Cove (west of Trevalga) are a 

 case in point. Here the Blue-Black Slates lie in their proper position 

 between the Volcanic Series below, and softer greenish phyllites with 

 white spots above ; but the slates form a mere zone in the cliff, the 



1 See W. M. Hutchings, Geol. Mag. 1889, pp. 106, 107. 



