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limestones, and "younger gneiss." His belief may still prove to be in some measure well founded. But at present we have no means of deciding whether the quartzites and limestones of the Central Highlands are the more altered equivalents of the undoubtedly Cambrian strata of the north-west. It is possible that in the vast mass of metamorphosed rocks constituting the wide stretch of country from the northern headlands of Aberdeen to the south-western promontories of Argyllshire, there may be portions of the old Lewisian gneiss, tracts of highly altered Torridon sandstone, belts of true counterparts of the Cambrian quartzites and limestones of Durness, and, what should not be forgotten, considerable portions of some later sedimentary series which may have followed these limestones, but which, by the great dislocations already referred to, have disappeared from the north-west of Scotland. We are gradually learning more of these rocks, as the detailed mapping of them by the Geological Survey advances, and when the ground on either side of the Great Glen is surveyed, it may be possible to speak with more certainty regarding their true geological relations.

A glance at a geological map of the British Isles will show that the metamorphic rocks of the south-western Highlands of Scotland are prolonged into the north of Ireland, where they spread over a region many hundred square miles in extent. They retain there the same general character and present the same difficult problems as to their true stratigraphical relations. Quite recently, however, a new light seems to have arisen upon these Irish rocks. My colleagues on the Irish Branch of the Geological Survey have detected several detached areas of coarse gneisses, which in many respects resemble parts of the Lewisian gneiss of north-west Scotland. In some cases these areas lie amidst or close to "Dalradian" rocks, but with that obstinacy, which so tries the patience of the field-geologist, they have persistently refused to disclose their true original position with regard to these. Some fault, thrust-plane, tract of boulder-clay or stretch of bog is sure to intervene along the very junction-line where the desired sections might have been looked for.