Vol. 59.] 



THE TINTAGEL AND DAVIDSTOW DISTEICT. 



423 



The darker bands are produced by the presence of a feebly 

 dichroic and inert chlorite, which forms an irregular network in 

 which lie crystals of clinochlore. This mineral occurs in lath-shaped 

 crystals with ragged terminations, plentifully besprinkled with 

 inclusions which are usually arranged along the central part, but 

 not sufficiently to obscure the characters of the mineral. Many of 

 the enclosures are minute prisms and granules, resembling rutile. 

 Cleavage is not conspicuous, and polysynthetic twinning is usual 1 

 (fig. 5). The extinction-angle between twins is about 12°. The 



colour for vibrations 

 Pig. 5. — PhyUite containing clinochlore, 

 X 40. Western end of Trewassa, near 

 Bavidstow. 



parallel to the basal 

 plane is grass-green ; at 

 right angles to this pale 



y ello wish - green . The 

 largest crystals measure 

 about *045 inch in length. 

 The mineral is distin- 





Maynard Hutchings has 

 kindly forwarded to me 

 his sections of ottrelite- 

 phyllite from near Tre- 

 vena Church, and I find 

 the two minerals to be 

 perfectly distinct. The 

 rocks invariably contain 

 haematite or some other 

 iron-oxide. In a field- 

 quarry near Davidstow 

 Vicarage the rock is 

 banded with arenaceous 

 laminae, a character com- 

 mon in the beds of the 

 group. A thin section 

 shows that prisms of 

 ** rutile occur in the clino- 



chlore and in the body of the rock. Some quantity of an opaque 

 granular mineral, probably haematite, and dusty-brown matter are 

 scattered through the slide. 



The Hallwell-Cottage Beds from other localities (as, for example, 

 Doney's Shop and Eosebenault, not far from St. Clether; and Benoath 

 Cove near Bossiney Haven) differ, but in minor details, from those of 

 Trewassa. Clinochlore characterizes the more typical rocks, favouring 



1 See A. Kenard, Bull. Mus. Boy. Hist. Nat. Bclg. vol. iii (1884-85) pp. 250 

 et seqq. ; J. S. Flett, ' The Geology of Lower Strathspey ' Mem. Geol. Surv. Expl. 

 of Sheet 85 (1902) pp. 48-40. 



