Carboniferous Scotland 359-299 million years ago

The Devonian time period is followed by the Carboniferous, during which Scotland lay at the equator. The Midland Valley area was covered in rainforest and the surrounding tropical seas had abundant fauna and thriving coral reefs. Rocks formed from the sediments and corals of the near-shore shallow-marine environments of the Carboniferous occur in the Lothians, Borders, Fife, Ayrshire and along the northern coast of the Solway Firth.

During the Carboniferous and also during the later Permian period, approximately 360-250 million years ago, Central Scotland was affected by north-south directed extensional stresses (or stretching). The stretching was linked to movement of the Earth's tectonic plates. Centred around what we know as the Central Belt, the stretching resulted in rifting and sinking of the continental crust to form Scotland's 'Midland Valley'. This is why the old geological foundations of the Central Belt have sunk down and are now buried by younger Devonian, Carboniferous and Permian rocks. The rifting of the crust was similar to that which is occurring in east Africa (the East African Rift) today. Rifting results in thinning of the crust, the thinning causing upwelling of magma from the underlying mantle.

Most of the magma came to the surface in the Central Belt along faults, fractures in the Earth's crust which had formed to accommodate the stretching. Erupted lava covered a large area forming lava fields such as the Campsie Fells. Arthurs Seat in Edinburgh and Dumbarton Rock represent the remains of early Carboniferous volcanoes.

Later in the Carboniferous, successions of sediments were laid down alternately in shallow seas and in rivers, in response to changes in sea level. Limestones, shales and sandstones testify to the changing environmental conditions. In estuary and swamp environments that became widespread in later Carboniferous times, coal deposits were laid down in the steamy tropical climate.