The Two Earth-Movements of Colonsay

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Abstract
The field-work which forms the basis of the present communication was carried out by Mr. E. B. Bailey and the Author in the summer of 1907, in the course of the geological survey of the island of Colonsay. The systems of folding displayed here and in the sister isle of Oronsay were found to possess features of more than usual interest, and special attention was given to the subject as far as the rapid nature of the work permitted. The investigation was facilitated by the rocky character of the islands, the surface of which is but little obscured by superficial deposits. A fairly continuous series of observations was thus rendered possible, and although a thorough understanding of the subject was by no means arrived at, yet certain facts came to light which may possibly have an important bearing on the orogenic history of the Highlands. For clearness and convenience of reference the subject will be discussed under the following heads:— I. The Stratigraphy and Chief Tectonic Features of the Islands. II. The Igneous Rocks. III. The Two Earth-Movements. IV. The Relation of the Earth-Movements to the Lamprophyres. V. The Relation of the Earth-Movements to the Plutonic Masses. VI. The Varied Age of the Lamprophyres. VII. The Nature of the Second Cleavage. The sedimentary rocks of supposed Lower Torridon age which form the greater part of Colonsay and Oronsay consist of an alternating

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