412 ME. J. PAKKINSOK ON THE GEOLOGY OF [Aug. I9O3, 



such a junction thin beds of ashes or small lava-flows are often inter- 

 bedded with the Black Slates, as, for example, to the east of Barras 

 Gug, where they are not more than a few inches thick, and continue 

 horizontally only for 10 or 12 feet. 



Quite possibly the rocks of the Volcanic Series may include later 

 basic intrusions, which have not yet been separated. 



At Barras Nose magnetite is locally very conspicuous, and on 

 Smith's Cliff rectangular crystals of marcasite three-eighths to half 

 an inch long are scattered through the rock. 



Above and below the Volcanic Series are the readily recognizable 

 Upper and Lower Blue-Black Slates ; but the arrangement of 

 the remaining beds is attended with some difficulty, owing to the 

 variation in the petrographical characters and the resemblances 

 often found between rocks of different horizons. 



The group underlying the lower slates, towards the x Hallw ell- 

 Cottage Beds, is distinguished, when typically developed, by a 

 line banding, accompanied, however, by considerable variation 

 from point to point. The rocks contain a clinochlore resembling 

 ottr elite. 



Good examples may be seen in the neighbourhood of Bossiney 

 Haven, parts of the Bocky Valley, Hallwell Cottage, Trewassa, etc. 

 These rocks are pale-grey in colour, speckled with unoriented 

 crystals of clinochlore, resembling carraway-seeds in the hand- 

 specimen. With a lens minute black specks of haematite can be 

 made out, and the mass of the rock has a saccharoidal appearance, by 

 reason of the interwoven flakes of sericite of which it is composed. 

 Such rocks are sufficiently soft to be marked by the nail, but they 

 are often darker in colour, and then commonly harder. 



Aggregation of clinochlore and filmy chlorite along certain lines 

 gives rises to the typical banding, and the lighter-coloured parts 

 not infrequently contain quartz-grains. These typical members of 

 the Hallwell-Cottage Beds are associated with unhanded dark and 

 more slaty rocks without clinochlore, breaking under the hammer 

 into sheets about three-sixteenths of an inch thick. Their foliation- 

 surfaces feebly reflect the light, and examination with a lens shows 

 them to be crystalline. Locally, they are speckled with small white 

 spots (as, for example, at Treknow and Bedevalleu), and then recall 

 the Tredorn Beds. Frequently these dark slaty rocks occur imme- 

 diately below the Lower Blue-Black Slates, as, for instance, on the 

 eastern side of the mouth of the Rocky Valley. 



Between the sea, at this point, and Trewethet the more typical 

 clinochlore-bearing beds come in at intervals along the side of the 

 valley and on the banks of the stream. 



On the east side of Bossiney Haven, the next inlet to the west, 

 well-banded beds occur immediately below the Lower Blue-Black 



1 On the 1-inch map midway between Hendra and the South-Western Kail- 

 way, 1^ miles north-west of Davidstow Church. Mr. Hutchings has described 

 ottrelite from near Tintagel Church, a part of the district that I have not 

 examined : see Geol. Mag. 1889, p. 215. 



