Page:Quarterly Journal of the Geological Society of London, vol. 35.djvu/846

706 Some of these fossils range upwards from the Caradoc or Bala stage: but the majority are solely Upper Silurian forms, ranging from the Llandovery to the Ludlow stages.

On examining the specimens in the collection of the Geological Survey, it appeared to me that the fossiliferous portions of the rock were curiously mixed up with fragments derived from metamorphic strata, such as quartz, mica-schist, &c, with which they could have no connexion. There can he no difficulty in accounting for the presence of such pebbles, as all the rocks older than the Llandovery stage are metamorphosed in the west of Ireland, and they probably formed the land-surfaces of the Upper Silurian period. But how are we to account for masses of coral, broken shells, and crinoids of Upper Silurian age, in company with such rolled and transported blocks? Many of these fossiliferous masses are angular, friable, and evidently not far removed from their original position. They could not have been derived from the fossiliferous Upper Silurian beds which crop out on the north-west coast, because these were buried underneath by several thousand feet of conformable strata. The conclusion, therefore, that I have come to regarding their presence is that they were really formed in situ, in immediate proximity to the place where they are found, but have been loosened, drifted, and somewhat broken up by the current-action, which carried the pebbles of older metamorphosed rocks, and strewed them over the sea-bottom.

I may add that the occurrence of this conglomerate is not regarded by Sir R. Griffith as an obstacle to the acceptance of the view of the Silurian age of the "Dingle beds." He remarks, "Cases of derivative rocks sometimes occur in the same continuous series; and such cases are rather to be expected, if we suppose the existence, at points not far distant, of the contemporaneous operation of agencies of denudation and deposition". On the whole it is impossible to suppose that these fossiliferous fragments could have come from strata of the Llandovery and Wenlock stages, which were buried under several thousand feet of these same "Dingle beds," both formations being conformable.

That the main mass of the Dingle beds reappears in the promontories of Iveragh, Dunkerron, and Bear, rising into the highest elevations of the south-western highlands, is now universally admitted, and cannot be questioned. The rocks are similar in character, consisting of hard massive green grits, sometimes conglomeratic, surmounted by great beds of purple slate with bands of grit. Whatever, therefore, may be the age of the Dingle beds in the promontory of Dingle, such will it be in the districts of Killarney, Kenmare, and Glengariff.

A difficulty has, however, been experienced by both Griffith and the Geological Surveyors in the attempt to separate these beds from