Wherever granite enters, it tears its irregular way through the opposing rocks, and sends veins through cracks where such occur. The result of its forcible entrance in a molten condition is that the contiguous rocks are melted, blistered, and baked by the intrusive matter. Why granite should differ from the lava we see exuding from active volcanoes is explained by the fact that it is formed deep below the surface where there is no outlet for its gases. It cools slowly and under great pressure and this gives it its special character. If found, therefore, at the surface, as it is in Aberdeen, this is because the rocks once high above it, concealing its presence have been worn away, which gives some idea of the great age of the district. One large granitic mass is at Peterhead, where it covers an area of 46 square miles, and forms the rocky coast for eight miles; but the whole valley of the Dee as far as Ben Macdhui, and a great part of Donside, consist of this intrusive granite. It varies in colour and quality, being in some districts reddish in tint as at Sterling Hill near Peterhead, at Hill of Fare, and Corennie; in other parts it is light grey in various shades. The succession in the order of sedimentary rocks is definitely settled, and although this has little application to Aberdeenshire, an outline may be given. The oldest are the Palaeozoic which includes—in order of age— Cambrian, Silurian, Old Red Sandstone or Devonian, Carboniferous, Permian. Of these the only one represented in Aberdeenshire is the Old Red Sandstone, which occupies a considerable strip on the coast from Aberdour to Gardenstown, and runs inland to Fyvie and Auchterless and even as far as Kildrummy and Auchindoir. The deposit is 1300 feet thick. A visitor to the town of Turriff is struck by the red colour of many of the houses there, a most unusual variant upon the blue-grey whinstone of the surrounding districts. The explanation is that a convenient quarry of Old Red Sandstone exists between Turriff and Cuminestown. Kildrummy Castle, one of the finest and most ancient ruins in the county, is not like the majority of the old castles built of granite but of a sandstone in the vicinity. The same band extends across country to Auchindoir, where it is still quarried. The next geological group of Rocks, the Secondary or Mesozoic, includes—in order of age— Triassic, Jurassic, Cretaceous. These are not at all or but barely represented. A patch of clay at Plaidy, which was laid bare in cutting the railway track, belongs to the Jurassic system and contains ammonites and other fossils characteristic of that period. Over a ridge of high ground stretching from Sterling Hill south-eastwards are found numbers of rolled flints belonging to the Cretaceous or chalk period, but the probability is that they have been transported from elsewhere by moving ice and are not in their natural place.