Vol. 59 .] 



THE TTNTAGEL AND DAVIDSTOW DISTKICT. 



419 



grass-green chlorite, without visible structure, in which lie [also 

 partly-altered plates of brown mica (fig. 4). A considerable propor- 

 tion of the slice (including some of the epidote-crystals) is rendered 

 opaque by dust of magnetite, specular iron, etc. associated with 

 granules of sphene and groups of rutile-prisms. In some slides the 

 latter mineral occurs in quantity. 1 The rutile appears to havejbeen, 



Fig. 4. — Crystals of epidote (enclosing allanite) and hiotite contained, 

 in a chloritic ' base/ X 40. From Bossiney Haven. 



[The section is cut parallel to the foliation.] 



on the whole, the first mineral to form, and was followed by mag- 

 netite and sphene. Epidote preceded biotite. Probably there was 

 but little difference in the times of formation of the first three 

 minerals. 2 



The initial steps in the production of epidote are shown in a rock 

 from Trambley Cove which seems originally to have been a diabase, 

 and in which an approximation may still be made to the several 

 areas originally occupied by the augite and felspar. Parts of the 

 slice are dappled with flakes of green mica, often vaguely outlined, 



1 See W. M. Hutchings, Geol. Mag. 1889, p. 104. 



2 See A. Harker & J. E. Marr, Quart. Journ. Geol. Soc. vol. xlix (1893) p. 364. 



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



