Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/34

 the place of contact is at present inaccessible. In the neighbouring colliery both portions of the vein hold their course through the seam there worked, and the coal is charred by their influence.

Some of the blocks from the quarry are quite black, and of an earthy fracture, and contain nodules of quartz and chalcedony, varying in magnitude from the size of a pin's head to that of a large pea. Other specimens of the rock are hard, coarse grained, and of an iron-grey colour; but in neither varieties have I found the mineral resembling adularia, so abundant in the basalt of Coley hill.

A basaltic dyke 6 feet wide may be seen among the rocks of the coal formation at the south-eastern corner of the promontory on which Tynemouth castle stands. Another, about 3 yards wide, appears in the cliffs near Seaton sluice; its direction is west-northwest, and it may again be seen in Hartley burn. A small whin dyke was formerly quarried near Bedlington; and another is found in Cowpen colliery, which has charred the coal in contact with it.

Passing to the south of Newcastle about 2 miles beyond Durham, a basaltic vein may be seen, when the water is low, at Butterby in, the bed of the Wear. This vein is remarkable for a salt spring that issues from its interstices, and for a string of galena (first noticed by Mr. Fenwick of Dipton) that fills a crevice beside it. Two miles further to the south near the junction of the Auckland and Darlington roads, is another dyke, the direction of which is nearly east and west, and on which two quarries are worked, each about 10 feet wide.

Of the Cockfield dyke a section and description have been given in the History of Durham, by the late Mr. Dixon, from which I work I derive the following particulars.

This dyke passes in a north-west and south-east direction from