Vol. 59.] THE TINTAGEL AND DAVIDSTOW DISTRICT. 427 



leucoxene and associated with a little sphene — apatite, and chlorite, 

 are the remaining minerals. 



In the rock from the field to the east of King Arthur's Hotel, 

 Tintagel, the hornblende forms large plates doubtless replacing 

 augite. The felspar is converted into an aggregate of decomposition- 

 products, but appears to have crystallized before the original augite. 

 Epidote is common, aud impure granular spheue is present in 

 quantity (ilmenite is absent). 



Conclusions. 



The contents of the preceding pages may be embodied in the 

 following conclusions : — 



1. That from St. Clether, as far as the coast south of Boscastle, 

 the Upper Devonian Beds (with Spirifera Verneuilii) have a fairly 

 uniform strike from east-south-east to west-north-west, with a 

 northerly dip ; but that along the coast in a southerly direction, from 

 the Rocky Valley to Trebarwith Strand, the higher beds again 

 appear, a result attained partly by north-north-easterly faults, partly 

 by an alteration of strike (see p. 409). 



2. That, the beds having acquired their present dip, subsequent 

 pressure resulted in great brecciation and contortion of the harder 

 strata, and in a general though less obvious compression of the 

 softer members : such pressure being locally relieved by differential 

 movement parallel to the dip (see pp. 409, 410). 



3. That the most distinctive rocks of the district are a series of 

 ashes and basic lavas, usually greatly altered, and not infrequently 

 entirely reconstructed, with the development of chlorite, white mica, 

 actinolite, sphene, epidote, allanite, etc. ; and that these were 

 deposited, at least in part, in a sea in which limestone was forming 

 (p. 417). These are called the 'Volcanic Series ' (pp. 411 & 414). 



4. That, with the exception of intrusive epidiorites, 1 the remaining 

 rocks of the district are sedimentary, and closely resemble the 

 phyllites of the Ardennes described by the late Prof. Renard. 



5. That these phyllites are distinguished by petrographical 

 features according to which they may be subdivided. 



These subdivisions are :— Comparatively thin beds of Blue-Black 

 Slates — including quartzose beds — above and below the Volcanic 

 Series ; the uppermost of these overlain by soft greenish-grey or 

 dark-grey phyllites containing a mineral resembling orthoclase in the 

 western part of the district; the lower underlain, in descending 

 sequence, (a) by banded phyllites, locally quartzose and containing 

 clinochlore (Hallwell-Cottage Beds) ; (6) by soft silvery-grey phyl- 

 lites, locally harder and darker, and sufficiently cleaved to be used 

 for slates, occasionally with quartzose bands (Penpethy Beds) : and 

 (c) by black, bluish, or greyish-black phyllites, locally containing 

 various contact-minerals (Slaughterbridge Beds). 



1 I except here also the rock described on p. 426 from Higher Trefrew, and 

 igneous rocks which occur locally above and below the Volcanic Series, as near 

 Tintagel. 



Q.J.G.S. No. 235. 2h 



