System cannot be of the age of the Old Red Sandstone. 131 



tiniiation from their great central area ; at the west extremity 

 of the tiiwn, by the turnpike gate on the Callington road, it 

 is killas, delicate pale-green killas. A few years since a 

 shaft was sunk in it there on a copper lode, which was suffi- 

 ciently productive for about sixteen fathoms deep ; below this 

 they came to a very black carbonaceous slate and grit beds, 

 where they lost the lode; they sunk the shaft into the same 

 black greasy shales and grits to the depth of forty fathoms, 

 but could neither sink through them or recover the lode. I saw 

 the black stuff as it came up in buckets, and could not well 

 doubt its identity with the same schist and shale 1 observed 

 both in and about the town. 



If we cross the river Tavy by the bridge almost behind the 

 Bedford Arms, and take the eastward road, we shall shortly 

 come to a quarry, and a little beyond it to a cutting a few feet 

 only above the river bed. The quarry is chiefly greenstone 

 trap, but it rests on and is parted by culmy schists, with 

 glance surfaces, which blacken the fingers; the cutting beyond 

 it is the s^ime slate and shale, which, like the beds in the 

 quarry, dip into the hill which rises steeply above us; that hill 

 is all killas ; a part of Whitchurch Down delicate gray, or 

 pale-green killas with quartz veins. 



From hence we must return to the broad range of Coddon 

 Hill grit, which constitutes the great south anticlinal line ; 

 near Greeston bridge, on the road from Launceston to Tavi- 

 stock, it bifurcates, as it were, into two ridges, in consequence 

 of their having intercepted a valley of killas about a mile in 

 width between them *, shown to be so by the fact alone of se- 

 veral shafts at Kelly having been sunk through the killas into 

 the subordinate Coddon Hill grit after its manganese. The 

 southern range of the grit, oftentimes apparent, sometimes 

 concealed by the floriferous or killas, extends in about an 

 east and west direction to Brentor, whence it is carried by an 

 easy curve to Lidford, where it corresponds with the anti- 

 clinal axis on the other side of Dartmoor, at Ashton and 

 Doddiscomb Leigh. The northern range is continued from 

 South Tregear and St. Stephen's Down to Lew Trenchard, 

 east and west, whence it curves parallel to the southern range, 

 striking off to the north-east, and conforming to the outline 

 of Dartmoor, which from Sourton and Sourton Tor, on the • 

 north-west of Amicombe Hill, is closely invested by it in one 

 broad uninterrupted zone, round to JVleavy on the south-east 

 of Tavistock. I have identified it in its true type, out ot the 

 melamorphic influence which the granite lias exercised on its 



• See Section, No. 2. 

 K2 



