Further to the south-east and in the line of the direction of the Walker dyke, a small quarry of basalt was formerly worked about 1 mile north of Boldon hills. The rock was fine grained, nearly black, and filled with small globules of milk white chalcedony, not bigger than a mustard seed.
With regard to the basaltic rocks of Coley hill, Walker, and Boldon, it is by no means well ascertained that they are portions of the same dyke, connected together below the surface; since no trace of that of Coley hill could be discovered in the very extensive and ancient collieries of Montagu and Kenton, situated in its course at a short distance to the east of it; nor was the Walker dyke found in any other colliery.
At Walbottle Dean, 5 miles west of Newcastle, below the bridge on the western road, a double vein of basalt[1] crosses the ravine in a diagonal direction, passing nearly due east and west. It hades to the north at an angle of 78°, and cuts the coal-measures without altering their dip. On the eastern bank of the ravine it is laid bare from the level of the brook to the height of about 60 feet. The northern and southern basaltic portions of the vein, the one 5 the other 6 feet in thickness, are there 13 feet apart, and are separated from one another by a confused heap of fragments of sandstone and shale broken from the coal-measures. With these fragments are found balls of basaltic tufa parting into concentric layers, and of a light yellowish brown colour: the balls are most abundant on the sides of the rubble near to the basalt.
Where the dyke reaches the surface a quarry of the basalt was formerly worked, which has lately been cleared. A small seam of coal meets the basalt at no great depth from the quarry-head, but
- ↑ Plate 4, fig. 2.
