Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/565

Rh rocks west of Millom, that its occurrence might be looked for in Ireland, where rocks appertaining to the Bala series are seen.

On the coast of the co. Dublin, the nearest locality where such rocks could be expected to appear, they are absolutely seen in the direct line of strike of the Coniston Limestone of the north-west of England.

On Lambay Island, two and a half miles east from the mainland, in the south-east portion of the island, we have part of the Coniston series forming a synclinal, though exhibiting many of the same features and the same fossils which this group of rocks in the Lake-district affords. Here are grey limestones succeeded by concretionary bands called by Mr. Du Noyer "coarse Conglomerates" (Explanations of Sheets 102 & 112 of the Maps of the Geological Survey of Ireland). This "Conglomerate" is described as "composed chiefly of rounded pebbles and boulders of grey Silurian Limestone, either fossiliferous or not, with fragments of dark cleaved state, grey grit and greenish grey greenstone, and ash: in one instance a boulder of an older Silurian Conglomerate was discovered, in which were rolled pebbles of a dark green close-grained greenstone, the base being a grey limestone containing Silurian fossils." (Note by Mr. Jukes:—"Some of the Silurian corals were attached by their bases to the pebbles, showing that they had grown on them, just as corals may now be seen growing on pebbles or fragments of rocks along a tropical shore.") "The matrix of the Kiln-Point Conglomerate is a black mud; and throughout the deposit are irregular slaty layers." "When we get lower into the mass we lose the conglomerate, and find nothing but pure dark grey slates, which, near Raven's Well, are found to contain Graptolites and thin calcareous fossiliferous bands" (p. 48).

It is also stated that at Kiln-Point the "grey Silurian Limestone is a wedge-shaped mass of lumpy layers, with thin bands of dark grey earthy shales between them, all very much contorted and resting on the porphyritic greenstone, which has evidently come up under them while in a pasty condition from heat, as it sends veins and strings into the lower beds of the limestone, and often enclosing fragments derived from it." Other circumstances indicate volcanic activity during the deposition of these limestones, even to a greater extent than has been recognized in the Lake-district.

These limestones have below them rocks intimately related to those of the Borrowdale series of the north of England, which are doubtless the equivalents of the latter.

At Portraine, on the mainland, immediately opposite Lambay, there is seen, on the coast, one of the finest sections of the Coniston Limestone and its associated rocks which occurs in the British Isles.

Portraine is about two miles east of Don abate Station, on the Dublin and Drogheda Railway. On reaching the coast an exposure of rock is seen a little east of the coast-guard station. This consists of a purple conglomerate, largely made up of quartz pebbles, which has been designated Old Red Sandstone; but it is more probably the basement conglomerate of the Carboniferous formation. As