Kildonan dyke swarm on Arran

On the beach at Kildonan at the south end of Arran there are a large number of these linear rock structures on the beach. They look like concrete sewage pipes at first glance but they are one of the most amazing bits of geology I've ever seen. About 60 million years ago basic magma - that's the type from which the oceanic crust forms - welled up through cracks in the sandstone rocks hereabouts. It solidified to form these dykes. They are tougher than the surrounding sandstone and so stand up like walls.

 Clearly such hot magma will affect the surrounding sandstone. See the picture above. There is something called contact metamorphism where the heat changes the existing sedimentary rocks. I suspect that's what has happened here. These sections are harder than the surrounding sandstone and have also resisted erosion.

 The dykes go on as far as the eye can see. I was amazed to discover that there are only 25 known dyke swarms on Earth. This is one of only 4 in Europe. Here, some of the dykes are basalt from the basic lava and some are dolerite. There was apparently some mixing with granite magma - the sort of molten rock from which continental crust is made.

The village seems to be based around the biggest dyke of all.