The rocks on the coast and islands around here are all volcanic in origin. Dating from the Carboniferous, around 350 million years ago.
Most are interbedded lavas and ash deposits, like this one. By the way, a tuff is a type of rock made from volcanic ash. Nice to put my degree to good use sometimes.
However, some other people like Uri Geller believe the islands have a mystical link to the Egyptian pyramids.
He liked the islands so much, he bought the one on the horizon http://site.uri-geller.com/why_i_bought_lamb_island

And last year I was freezing.