Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/119

 a hillock one quarter of a mile east of Gale Hall, and between one and two miles south-east of Melmerby. The slate is cut by a broad dyke, of which the direction is nearly east and west, and its breadth about 25 feet. The substance of this dyke is composed of reddish compact felspar mixed with talc, and the latter becomes more bright and distinctly visible where the rock has undergone decomposition.

Under the south base of Knock pike close to the Swinedale Beck is a small portion of rock composed chiefly of dark mica, occasionally interspersed with small crystals of felspar, disseminated uniformly through the mica. On this lies a mass of highly compact whitish felspar and coarse greenstone.

On the summit of this Pike, which is nearly conical, and steep on all sides, is an outlying hummock of coarse grained sandstone, agreeing in substance with one of the lowest strata in the neighbouring escarpment, and more recent than the old conglomerate. Whether this latter rock, or any traces of slate, are interposed between the summit of the pike and greenstone of its base, we had no opportunity to ascertain. I have specimens of the grit taken from the summit.

At the west root of Dufton pike, in a field called Banky Close, and surrounded on all sides by greenstone, is a species of granite that is extracted to build field walls. It consists of bright salmon coloured felspar, in which are disseminated at very irregular intervals plates of bright silver coloured mica, varying in diameter from an inch to a line, and interspersed with a few small specks of quartz. This granite was so covered as to be visible only at a small ridge where the quarry was wrought. It might either be the projecting crest of a subjacent fundamental mass, or it may be a dyke cutting through the greenstone. In the quarry it is 15 yards broad, and