Broadly speaking the area can be divided into three bands, the divisions between which run south west to north east. Generally speaking the rocks become younger from north west to south east. The north western band is composed of early to mid-Ordovician sedimentary rocks, largely mudstones and siltstones of marine origin. Together they comprise the Skiddaw Group and include the rocks traditionally known as the Skiddaw Slates. Their friability generally leads to mountains with relatively smooth slopes such as Skiddaw itself.