Ingleborough. Part II. Stratigraphy

Abstract

The oldest rooks of which we have any representatives in this area are the great mass of green slates and grit and conglomerate which form the floor of Chapel-le-dale, and of Ribblesdale for about half a square mile near Horton. These so much resemble the old volcanic series described under the general title of “Green Slates and Porphyry” in the Lake District, and agree so well with them in their relation to the rocks with which they are associated, that, in default of any evidence to the contrary, they have been referred to the same horizon. The rock consists, as far as the finer parts are concerned, of fine felspathic dust: the grit is composed chiefly of grains of quartz and pink orthoclase in a greenish matrix consisting of finer grit and the same material as the slate. There are also, but rarely, beds of breccia much like those in the Borrowdale Series. Iron pyrites occurs in beautifully perfect cubes, and as dendrites in the slates, while the iron pervades the whole as a green silicate which is especially conspicuous in some of the more crystalline quartz veins. No fossil has ever been found in their equivalents in Cumberland; and, though these Yorkshire beds are more promising than those of the Lake District, no fossil has yet been recorded from them. The black marks seen on some faces of rock in the slate quarry north of Ingleton, which by their outline suggested graptolites, are merely segregations of mineral matter; while ...