Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/387

 Mr. Evans agreed with the author as to the difficulties presented by the Lake theory in accounting for the terraces, especially those not in Glen Roy itself, but in the valley of the Spean. He called attention to the part which sheep and other animals had played in the preservation of the Parallel Roads, the vegetation on which, in consequence of their being more frequented by the animals, was of a different character from that on the other parts of the slope.

Mr. H. M. Jenkins objected to the supposition of the sudden alteration in the level of the water adopted by the author. He thought the gradual sinking of the water was quite compatible with the formation of the roads. He instanced the formation of terraces in gravel-pits filled with water.

Sir H. James announced that the Ordnance survey of the district in question was now complete.

4. On Beds of supposed Rothliegende Age, near Knaresborough, &c. By J. Clifton Ward, Esq., F.G.S., of the Geological Survey of England and Wales.

By permission of the Director- General of the Geological Survey lam enabled to lay before the Society a brief outline of some observations made during the past summer in the course of my professional duties.

In the neighbourhood of Knaresborough occur certain very well- marked and distinctive grits of a red or purplish-red colour ; for the most part these rocks are coarse, frequently quite conglomeratic; oftentimes, however, they are mere sandstones, while in some places they pass into sandy shales. In some localities, as near Plumpton, the proportion of red felspar in the grit is very great, while in others white specks of decomposed mineral matter are scattered profusely through the mass. The quartz-pebbles are very often as large as pigeons' eggs, and form well-marked layers, generally at the base of the separate beds of grit.

The grit in the neighbourhood of Plumpton, near Knaresborough, forms most picturesque weathered masses. Between Spofforth and Plumpton, on the slope immediately below the magnesian-limestone escarpment, stand numerous detached pillars and masses of rock, some rising 15 feet above the level of the surrounding ground, others but barely protruding, their surfaces presenting all those curiosities of atmospheric action, in the shape of perforations, basin - holes, honeycombing along the planes of bedding, &c., which, although in many cases difficult to explain fully, yet seem still to be in process of forming. The soil of the fields in which these detached and picturesque rocks rise consists, as one would expect, of the decomposed grit, and seems of a very shifting nature.

On the age of this Plumpton grit I wish now to offer a few remarks. By some geologists it has been described as Permian and the equivalent of the Rothliegende of the Germans ; by others it has been assigned to the millstone -grit series.

1. Authorities for Permian Age. — Prof. Sedgwick (in his paper upon the magnesian-limestone series in vol. iii. of the 'Transactions' of this Society) speaks of these rocks as forming the base of