Magma rises up through the Earth’s crust

Rock, such as the Manx Group is intruded by the magma

Fissures form ahead of the rising magma.
These may cool and form dykes

Magma is molten rock sourced from tens of kilometres below the Earth’s surface.
It may cool and solidfy at lesser depths within the crust to form granite or gabbro, depending on its composition.

Granite originates tens of kilometres beneath the earth’s surface. Under the high temperature and pressures deep within the earth’s crust, rock can melt to form magma. Once this occurs, the magma may begin to rise up through the crust in a large body called a batholith. As the batholith rises it begins to cool causing minerals to crystallise out from the liquid magma. If the magma cools sufficiently, it eventually solidify completely and cease to rise. If the magma was originally rich in silica it will form a granite or if it was poor in silica it will cool to form a rock called gabbro. Over tens of millions of years, the rock above the solidified batholith may be eroded away leaving the granite or gabbro exposed at the surface, such as the Foxdale granite or the Poortown gabbro.