Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/561

1869.] NICHOLSON—IGNEOUS ROCKS OF THE LAKE-DISTRICT. 437 crystals of red felspar and many crystals of quartz, most of which are doubly prismatic. The width of the dyke is about 50 or 60 feet, and for three or four feet on both sides it is altered by contact with the trap through which it cuts. In this altered zone it becomes a compact red felstone, with a few crystals of quartz scattered through it, but without any crystals of felspar.

II. The Syenitic Porphyry between Ennerdale mid Buttermere.

This syenitic felstone-porphyry forms an intrusive mass of very considerable extent, occupying an area of about six miles from east to west by about three miles from north to south, comprising the mountainous district between the lakes of Buttermere and Ennerdale, the lower half of the valley of the Liza and the mountains to the south of Ennerdale Lake. Commencing at Bowness, a small hamlet situated about midway between the extremities of Ennerdale Water on its north-eastern side, the syenitic porphyry is seen to form Bowness Knot, and to be immediately succeeded on the N.W. by the Skiddaw Slates, which are greatly metamorphosed, and are converted into a hard greenish-grey rock, very compact, and exhibiting few traces of bedding. On the opposite, or south-western, side of the lake the syenitic porphyry is continued nearly to the foot of the lake, being probably shifted to the N.W. by a fault. It forms here the hills known as Crag Fell (or the Revelin) and Angler's Crag, and it is succeeded on the N.W. by the Skiddaw Slates, which form the northern flanks of Grike Fell. From their junction with the syenite for a distance of nearly three-quarters of a mile the Skiddaw Slates are highly metamorphosed, retaining no signs of their sedimentary origin beyond the existence of lamination. They are converted into an extremely hard, granular rock, much penetrated by quartz-veins, of a pink or greenish-grey colour, and finely banded along the lines of lamination. As just stated, the metamorphism in this locality affects a great thickness of the rocks, slates of the normal character not reappearing till Fell End is nearly reached. Returning to Bowness, the boundary of the intrusive rock can be traced between Ennerdale and Buttermere, pretty nearly coinciding with the road between these two lakes by way of Floutern Tarn. Between these points the syenitic porphyry is succeeded to the N.W. and N. by the Skiddaw Slates, and rises on the S.E. and S. into the elevations of Herdhouse, Great Borne (2019 feet), and Gale Fell.

About a mile and a half from Buttermere the cascade of Scale Force is formed over a precipice of this rock. From the foot of Buttermere the intrusive rock can be followed along the south-west margin of the lake, nearly as far as the pass of Scarf Gap. All along this line the Skiddaw Slates are seen striking right against the porphyry, and more or less metamorphosed near the line of contact. The metamorphism does not appear to extend more than a few feet from the porphyry; but within this zone the slates are converted into a hard, laminated, greenish-grey rock. To the S.W. of this