Extract

The Isle of Arran has long been looked upon as the happy hunting-ground of geologists, the number and variety of its rocks, both igneous and aqueous, making it almost an epitome of the geology of Scotland. The northern part of the island, with its granite core and ring of metamorphic rocks, has been fairly well represented on the geological maps, but the plexus of intrusive rocks in the southern part has been till lately simply a chaos, and no serious attempt was made to resolve it … .¹

Schists.—The foliated schists which nearly surround the granite are by far the oldest rocks in the island, but their exact age is not known. They are a part of the great metamorphic series which stretches all across Scotland from Aberdeenshire to Kintyre, and almost everywhere the excessive crumpling of the foliation planes and the abundance of quartz in strings and veins are common phenomena, so that these are not due to the intrusion of the granite, as many of the earlier writers supposed. The rocks are similar in character to those which occur in Bute and Argyle on one side, and in Kintyre on the other, in districts where there is no granite intrusion. They are generally called slates by previous writers, but slates form only a part of the series of rocks, many of them being coarse and gritty schists or schistose pebbly grauwackes. The foliation planes must not be taken everywhere for the bedding, as sometimes there is a considerable