344 The Rev. D. Williams on the Killas Group of 



the beds are seen to be no longer affected by the high angle 

 of dip which had displayed the entire series in such minute 

 detail and fine succession on the Tamar (as it also does from 

 Endellion to Constantine bay on the west of Padstow), but 

 they have settled down to so low an inclination as has per- 

 mitted the metalliferous series No. 3 to be expanded over 

 a great portion of the intermediate area, from a mile or two 

 north-west of St. Germans to nearly three miles north of 

 Liskeard. 



A similar phasnomenon may be observed on the north-west 

 of Bodmin, over a considerable area where the upper gray 

 calcareous beds of No. 2, being sometimes apparently flat, or 

 at others inclining at a very low dip, conceal all the subor- 

 dinate variegated beds, until between St. Mabyn and St. Tudy 

 a higher angle brings up the blue, purple, green and gray 

 slates, which range continuously from thence by Endellion, 

 St. Minver, and St. Enodock, in a thick zone, to the north 

 and west of Padstow. 



No. 1, the Tintagel or Clymenien killas, is of perfectly 

 unique mineral type, and a certain proportion of its fossils are 

 as yet equally appropriate and characteristic : it is almost uni- 

 formly a delicate pale green or greenish-gray slate, rarely a 

 blueish-gray, with quartz veins, commonly crystalline, — some- 

 times highly so: it is more or less calcareous throughout, but 

 its nether division from Tavistock on the east to Trevalga and 

 Tintagel on the west, contains masses of varying dimensions, 

 — oftentimes continuous for many miles together — of a highly 

 calcareous hornblendic and chloritic volcanic ash, which, on 

 decomposing, always constitutes a fertile soil; and at Brad- 

 stone, Kelly, Milton Abbot, Lamerton, and on the north of 

 Tavistock, affords some of the richest land in England. 



That it forms the basis and supports the great killas super- 

 structure, is abundantly shown by explicit sections on either 

 side the Tamar, at inland quarries and cuttings, and on the 

 westward coast on the south of Port Isaac, where it passes in- 

 sensibly into No. 2 by neutral and alternating beds, and in- 

 disputably underlies it. 



It yields tin and copper near Tavistock and Callington, 

 and lead and silver are worked in it to a greater extent than in 

 either of the killas series above it : excellent roofing-slates 

 are also quarried in it at Tintagel and Delabole on the west, 

 and at Mill-Hill near Tavistock on the east, and they have 

 also been proved at several intermediate points. 



It passes into great lentiform bunches of lime-rock at Tre- 

 nalt and Petherwin near Launceston, which rest on, and are 

 parted by, black anthracitic slates, with thin layers of culm, 



