Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/841

 stone. Above this point the stream cuts, for about a quarter of a mile, through glacial drift containing many blocks of trap and pieces of Skiddaw Slate. Here a little stream flows into the Lowther from the west, and exhibits the Skiddaw Slates a good deal contorted, but dipping on the whole S.S.E. These are almost immediately succeeded by a greenish-grey fine-grained felspathic trap, which forms the base of the Green-slate series. This is sometimes slightly hornblendic, and with some coarse ashy-looking beds occupies the ground up to the mouth of Keld Beck, also flowing into the Lowther from the west. Nearly half a mile to the south-east of Keld Beck is a third tributary, called Thornship Beck ; but the ground between these two streams is moory, and exhibits only a few scattered bosses of trap. In Thornship Beck, at its head, are seen bedded felspathic ashes, sometimes purple, sometimes green, with veins of quartz, and nodules of bright red jasper, and having intercalated amongst them one or two beds of trap. In the lower part of Thornship Beck the Skiddaw Slates again come on, and have been worked for slate- pencils. Their appearance here would appear to be most probably due to faulting, the dip varying a good deal ; but at the quarries there is a small anticlinal. The country to the south-west of Thornship Beck is very moory, and no rocks are seen in situ except a small exposure of a greenish-grey felspathic trap at the mouth of Thornship Beck. The termination upwards of the Skiddaw Slates is therefore not seen. The next exposure of rock is at a farmhouse called Kemp-how, situated on the Lowther, about half a mile to the south-west of Thornship Beck. Between this point and Cragg's Mill there is a fine section of some of the lower beds of the Green-slate series, consisting entirely of ashes and breccias, all highly cleaved. Some of the ash-beds have the ordinary characters of the " green slates ;" others are breccias, in which the included fragments consist entirely of ash ; and others are amygdaloidal, containing numerous sinuous vesicles, which are either empty or filled with quartz. The strike of the beds is a good deal deranged, varying from S.S.W. and N.N.E., through E.N.E. and W.S.W., to nearly due W. and E., the cleavage throughout being nearly vertical.

From the position of these beds there can be no doubt of their being the equivalent of the great slate-band of Honister and Borrowdale ; and they thus afford a useful guide in mapping this region. They can be traced to the south-west along the northern side of Wet Sleddale, through the higher part of Swindale, across the head of Long Sleddale (in the Gatesgarth Pass), across Kentmere (near the Reservoir), and across the head of Troutbeck ; and I have little doubt of their identity with the great band of slates which is worked between Rydal and Grasmere, and again still further to the southwest in Tilberthwaite, and in the Dunnerdale Fells. In all these localities I believe that these slates point to an horizon very close to the base of the whole series of the Green Slates and Porphyries, though not far removed from the southern limits of the great area occupied by this formation.