The granite mass of Dorback in the Braes of Abernethy, a few miles east of the village of Tomintoul, occupies an area of from 5 to 6 square miles, the plutonic rocks outcropping through the siliceous schists and granulites of the Central Highlands of Scotland. For a highland district the exposures are rather poor, since the igneous rocks only rarely appear from under a thick covering of peat and glacial drift, but towards the eastern margin of the mass the complex is well exposed in the valleys trenched by the Allt Iomadaidh and tributary streams. Here the interest of the plutonic rocks is twofold, for they form a complex of acid, intermediate, and basic types exhibiting considerable variation in petrography, and they include a series of xenoliths of quartzite, schist, and limestone which range from a few inches in diameter to a great mass of limestone 1½ miles in length. This xenolith has been mapped by the Geological Survey of Scotland, and it was the occurrence of a contact between limestone and plutonic rocks at this locality that led to the investigations of the authors.