The Swedish bedrock mainly consists of Precambrian gneisses and granites. The various sediment that were subsequently deposits during the Cambro-Silurian periods have to a large extent been removed by erosion. In some areas, however, they have been preserved in fault graben or by an overlying impervious blanket of diabase. The Cambro-Silurian sediments consist, from bottom to top, of sandstones followed by formations of black shales, limestones and grey shales. Sedimentary rocks from younger periods are only found in Scania, the southeasternmost province in Sweden.