Vol. 59.] THE TINTAGEL AND DAVIDSTOW DISTRICT. 425 



road leading from Camelford Station to Trebarwith Strand in the 

 neighbourhood of Penpethy (1-inch map). 



In the Prince of Wales's Quarry the dark phyllites split readily 

 into thin slabs, with a silvery lustre on their foliation -surfaces. 

 They are rather harder than the nail. The rocks consist of minute 

 scales of a green chlorite lying in a colourless ' base.' The latter 

 frequently frees itself from the less translucent mineral, producing 

 a mottled aspect in the slide. Minute flakes of white mica can 

 be detected by means of their higher polarization. Specks of iron- 

 oxides (hsematite and ilmenite) are important constituents, and 

 rutile, zircon, and tourmaline 1 are not uncommon. 



In many instances the last-named has exceptionally perfect 

 crystal-faces. Elongated fibrous crystals of a brown colour, not 

 pleochroic and with no effect on polarized light, are common, and 

 appear to be authigenous. They are often surrounded by a fringe 

 of chlorite. 



Microscopically the rock of Condolden Quarry (between Penpethy 

 and Waterpit Down) is identical with that of Higher Pendavey 

 Quarry described below. 



A grey grit occurs to the west of Lower Penpethy, composed of 

 a mosaic of quartz-grains — subangular and interlocking, no doubt 

 through secondary additions — in which lie flakes of green mica and 

 sericite. I have noticed no felspar-remnants. Since the micas are 

 clearly not detrital, the rock provides evidence of a considerable 

 reconstruction. Flakes of ilmenite are a common accessory, and 

 some of haematite. 



The Slaughterbridge Beds. 



The rocks of this group are black or bluish to greyish-black 

 phyllites, locally greatly crushed, and in some places altered as 

 though by contact-metamorphism, as, for instance, in the cutting 

 south of Yillaparks and on Griggs' Down. In the majority of thin 

 sections of the dark phyllites collected near Trekeek, Villaparks, 

 and Slaughterbridge, a close resemblance can be traced to some 

 member of one of the overlying series : that is, these rocks possess 

 no very definite characteristic of their own. 



In the phyllites from Yillaparks, Higher Pendavey, and around 

 Slaughterbridge, minute fibres of a greenish chlorite, intermingled 

 with a variable quantity of white mica, constitute the major portion 

 of the slides. Through this groundmass larger stumpy crystals of 

 white mica and rods of micaceous ilmenite are scattered. At Yilla- 

 parks, as to the north of Tregrylls, white spots characterize the 

 hand-specimens, but are often ground-out in thin slices. 



In the quarry at Griggs' Down, Davidstow Moor, a phyllite is 

 found, closely resembling in its general structure the rocks around 

 Slaughterbridge, in that it consists of a closely-knit intergrowth of 

 minute flakes of chlorite and mica, through which are scattered 



1 See A. Eenard, Bull. Mus. Eoy. Hist. Nat. Belg. vol. ii (1883) p. 132. The 

 form of the tourmaline-crystals from Penpethy is the same as that which 

 the late Prof. Eenard described. 



