Describe the characteristics and explain the formation of one or more intrusive volcanic features (June 2016)

Batholiths are the largest example of intrusive volcanic features, when magma enters the earths crust without enough pressure to break the surface, it pools to form a roughly spherical lump of rock often more than 100km in diameter. Usually it is composed of granite or similar rocks. It has a large grain size due to its slow cooling. An example is Lizard Point Batholith, Cornwall UK. Similarly to batholiths, sills are an example of historical volcanic activity, they occur when magma pools horizontally in the earths crust, it has smaller crystals than a batholith because its cooling is faster. A sill, like most intrusive features it more resistant to erosion than the surrounding rock so becomes exposed over geological time as the ground wears away, the emergence of Great Whinn Sill in England provided the basis for parts of Hadrian's Wall. Dykes are similar to sills except that they are  vertical rather than horizontal, and occur in groups known as dyke swarms. Plutons are small pools of magma that intruded into the crust from dykes and sills, they cool fastest so have the smallest crystals. Furthermore laccoliths may form when pools of magma under high pressure, push into the layer of sedimentary rock above them to create a mushroom-like dome shaped feature.