Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/86



At Bamborough 9$$\scriptstyle \frac 12$$ miles north-north-west of Dunstanborough, a well was sunk in the Castle hall to the depth of 150 feet, by which it was ascertained that the overlying rock of basalt was 75 feet thick, and rested upon a fine grained red and white sandstone, parts of which fell into small round fragments on being immersed in water.

In the Heugh, the promontory on which Holy Island Castle is built so as to command the harbour, the basalt seems also to rest on a soft fine grained sandstone; on the east side of the island the sea has scooped deep caverns in the latter rock; trials have there been made for coal, and small quantities of galena have been discovered, as I have before mentioned.

Basaltic dykes, which occur in the Coalfield, are also found intersecting the lead mine measures, instances of which may be seen on Aldstone moor, in Allendale, and in Weardale. A well defined dyke may be seen a little above South-Tyne-head smelting-house, traversing the Tyne bottom limestone without altering its level. The dyke is there 36 or 37 feet wide, and is by many thought to be the same that crosses the Allen close to the bridge at Whitfield and the Wear at Burtree-ford still further to the south. This basalt is of a coarse grained texture and greenish black colour. At Egglestone three miles below Middleton a very strong vein of basalt may be seen crossing the Tees in a diagonal direction; and the mountainous moors in the upper part of the vale are covered with fragments and immense blocks of this species of rock for the distance of many miles.

I have already mentioned that the basalt appears to fill dykes at Stagshaw bank and at Jemming. Further to the north, in the village of Embleton, not far from Dunstanborougb, an extensive quarry is worked in a basaltic dyke. The course of the vein is north and south, about a mile to the west of the craggy ridge on the sea coast,