Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/832

 thickness of the series is more than some 5000 or 6000 feet, though it doubtless varies considerably in different parts of this area.

It is the object of this communication to describe shortly some of the sections in the lower portion of the series of the green slates, as indicating the general lithology of the inferior division of the group. For this purpose I shall confine myself chiefly to the sections which are exhibited between Ulleswater and Derwentwater.

I. Lower portion of the Green Slates and Porphyries in Borrowdale.

The whole of the western side of Derwentwater, to the south of the little wooded hill called Rosetrees, is composed of the Skiddaw slates, which dip persistently to the S.S.E., at angles of from 40° to 60°, through Cat Bells, Barrow Side, Maiden Moor, and Narrow Moor, to about a mile to the S.S.E. of Manesty, near a farm-house called the Hollows (fig 1). The Skiddaw slates also form the flat ground at the head of the lake, extending as far south as the village of Grange, and occupying a narrow strip of ground on the western side of the river Derwent. The Skiddaw slates are succeeded to the south by the lowest member of the green-slate series, which is well exhibited in the northern end of Low Scawdel, to the east of the Derwent, and in Grange Fell on the west. It is a massive, dark green, compact, and fine-grained felspathic trap, in places rudely columnar, and exhibiting no distinct crystals of any kind. This trap is directly overlain by a great band of slates and breccias, which have been worked on both sides of the river in various places, and which form Goat Crag, Castle Crag, and the southern end of Grange Fell. The largest quarries are a little to the north of the Bowder Stone. "Wherever they have been worked these slaty beds are seen really to be a cleaved felspathic breccia, of which some beds are so fine-grained as to lose their brecciated nature ; whilst others consist of numerous angular fragments, from a quarter of an inch in diameter upwards, imbedded in a light-green felspathic matrix. The fragments in the breccia are mostly of felspathic ash or trap ; but many are very like pieces of Skiddaw slate. Subordinate to the bands of slate and breccia are some minor beds of trap, one of which near the Bowder Stone exhibits numerous small veins of epidote. The highest beds of the whole of this slaty series are amygdaloidal ashes, the cavities of which are mostly filled with quartz.

A similar sequence of rocks is exhibited a few miles to the S.W., in the valley of Gatesgarth Beck, which flows into the head of Buttermere. In proceeding from the head of Buttermere into Borrowdale, by way of Buttermere Hawse, the lower portion of the Gatesgarth valley is found to be occupied by the Skiddaw slates, which dip S.S.E., at from 50° to 60°, forming Buttermere Fell and the N.W. end of Honister Crag. At Dale Head the Skiddaw slates are succeeded by the lowest member of the green slates, in the form of a fine-grained dark-green felspathic trap, rudely bedded, and crossed at one point by a nearly vertical dyke of intrusive greenstone. This is overlain by a great series of cleaved felspathic ashes, amyg-