The Geological Survey has recently formed a very extensive collection of the dyke-rocks of Galloway. This collection was made mainly by Mr. Robert Eckford, and, to a less extent, by Mr. Wm. Manson. One or more specimens were taken of practically every dyke shown on the original 6-inch field-maps. Since there are over 500 collected dykes in Wigtownshire alone, the size and importance of this collection is apparent. A dyke-suite of this magnitude, so thoroughly collected without the personal bias of the petrographer, supplies unique material for study. By the kindness of Sir John S. Flett, F.R.S., Director of H.M. Geological Survey, I have been permitted to investigate that part of the collection coming from Wigtownshire. This Wigtownshire portion consists of considerably over 1,000 rock-specimens, nearly 200 of which have been sliced. In this present paper I propose to give an account of the distribution and petrography of one group—the mica-lamprophyres—of the Wigtownshire dyke-rocks.