The Tertiary basalt-plateaux of Britain have their counterpart in the Faroe Islands and in Iceland, and whether or not the lava-fields stretched throughout North-western Europe from Antrim to the farthest headlands of _Ultima Thule_, there can hardly be any doubt that, if not continuous, these volcanic areas were at least geologically contemporaneous in their activity. Their characteristic scenery and structure are prolonged throughout the whole region, reappearing with all their familiar aspects alike in Faroe and in Iceland. I have not seen the latter island, but in the Faroe archipelago I have found the dykes to be sufficiently common, and to cut the basalt-plateaux there in the same way as they do those of the Inner Hebrides. On the whole, however, dykes do not play, in these northern isles, the important part which they take in the geology and scenery of the West of Scotland. I have not had sufficient opportunity to ascertain whether there is a general direction or system among the Faroe dykes. In the fjords north of Thorshaven, and again along the west side of Stromö, many of them show an E. and W. strike or one from E.N.E. to W.S.W. 2. TWO TYPES OF PROTRUSION The dykes are far from being equally distributed over the wide region within which they occur. In certain limited areas they are crowded together, sometimes touching each other to the almost entire exclusion of the rocks through which they ascend, while elsewhere they appear only at intervals of several miles. Viewed in a broad way, they may be conveniently grouped in two types, which, though no hard line can be drawn between them, nevertheless probably point to two more or less distinct phases of volcanic action and to more than one period of intrusion. In the first, which for the sake of distinction we may term the Solitary type, there is either a single dyke separated from its nearest neighbours by miles of intervening and entirely dykeless ground, or a group of two or more running parallel to each other, but sometimes a mile or more apart. The rock of which they consist is, on the whole, less basic than in the second type; it includes the andesitic varieties. It is to this type that the great dykes of the north of England and the south and centre of Scotland belong. The Cleveland dyke, for example, at its eastern end has no known dyke near it for many miles. The coal-field of Scotland is traversed by five main dykes, which run in a general sense parallel to each other, with intervals of from half a mile to nearly five miles between them. Dykes of this type display most conspicuously the essential characters of the dyke-structure, in particular the vertical marginal walls, the parallelism of their sides, their great length, and their persistence in the same line.