The geology of Aberdeenshire is almost entirely concerned with igneous and metamorphic rocks. The whole backbone of the county is granite which has to some extent been rubbed smooth by glacial action; but in a great part of the county the granite gives place to metamorphic rocks, gneiss, schist, and quartzite. A young geologist viewing a deep cutting in the soil about Aberdeen finds that the material consists of layers of sand, gravel, clay, which are loosely piled together all the way down to the solid granite. This is the glacial drift, or boulder clay, a much later formation than the granite and a legacy of what is called the great Ice Age. Far back in a time before the dawn of history all the north-east of Scotland was buried deep under a vast snow-sheet. The snow consolidated into glaciers just as in Switzerland to-day, and the glaciers thus formed worked their way down the valleys, carrying a great quantity of loose material along with them. When a warmer time came, the ice melted and all the sand and boulders mixed up in the ice were liberated and sank as loose deposits on the land. This is the boulder clay which in and around Aberdeen is the usual subsoil. It consists of rough, half-rounded pebbles, large and small, of clay, sand, and shingle, and makes a very cold and unkindly soil, being difficult to drain properly and slow to take in warmth. Below this boulder clay are the fundamental rocks. At Aberdeen these are pure granite; but in other parts of the county they are, as we have said, metamorphic, that is, they have been altered by powerful forces, heat and pressure. Whether they were originally sedimentary, before they were altered, is doubtful; some geologists think the crystalline rocks round Fraserburgh and Peterhead were aqueous. Mormond Hill was once a sandstone, and the schists of Cruden Bay and Collieston were clay. The same beds traced to the south are found to pass gradually into sedimentary rocks that are little altered. Whether they were aqueous or igneous originally, they have to-day lost all their original character. No fossils are found in them. These rocks are the oldest and lowest in Aberdeenshire. After their formation, they were invaded from below by intrusive masses of molten igneous rock, which in many parts of the county is now near the surface. This is the granite already referred to. Its presence throughout the county has materially influenced the character and the industry of the people.