Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/566

480 such it has its representatives well exposed under the Carboniferous Limestones along the eastern margin of the Lake-district, and also under the Pennine escarpment.

A short distance east of the conglomerate a porphyry, having a delicate purple tint and containing well-developed crystals of a greenish white felspar, occurs. This porphyry is similar to that which forms the bulk of Lambay. Its purple tint is doubtless due to staining from the purple conglomerate which, in some places, overlies it.

Fragments of a similar purple porphyry are met with in the Lake- district near Caldbeck; and in some spots this porphyry is seen in situ overlain by purple conglomerates, when it manifests the same tint as the Portraine porphyry.

The Portraine porphyry is succeeded by traps and ashes; and these are seen to occur to beyond the farm-house on the coast.

At the farm-house the coast trends for a short distance south-east. A little beyond this the ash-beds begin to exhibit trappean fragments in them, the ashes assuming the nature of ash-breccias. The trap fragments, however, are not the only substances which the ashes contain; calcareous nodules also make their appearance in them.

Patches of black shale, which show no traces of volcanic origin, are also associated with the ash-beds; and these black shales afford Graptolites (Climacograptus teretiusculus). These ash-breccias with calcareous nodules and graptolitic shales prevail in greater abundance higher in the series; and in the cliffs under the Martello tower they are seen to be succeeded by fine green-coloured shales so much affected by cleavage that their bedding can scarcely be made out. There are some small faults indicated by Mr. Du Noyer as occurring between where the porphyry is seen and where the green shales make their appearance. These, however, are not of sufficient importance to render the section difficult to interpret. The green shales contain limestone nodules in bands which, though much contorted, indicate distinctly the lines of bedding of the shales, these shales being, no doubt, of ashy origin. Fossils occur in these nodules and also in those which are found in the ash-breccia; and these fossils are distinctly of a Bala type.

The "conglomerates," before referred to as seen on the south-east side of Lambay Island, are a portion of the ash-breccia series. They afford the same fossils, and they have the same graptolitic shales accompanying them.

As regards the horizon in which the nodular ash-breccias occur, as compared with the rocks of the north of England between the Borrowdale group and the Coniston Flags, it would seem that they must be placed on a parallel with those of Style-End Grassing and with the more amply developed Dufton shales. To the latter they are in part allied by their black shales, and to the former by their ashy nature. They indicate more violent volcanic activity in the locality of their deposition than the Dufton shales, but less powerful igneous influences than in the case of the Style-End Grassing ash-beds, where no black shales occur.