The Mendips are a range of hills in central Somerset, approximately 40km from top to bottom and 8km across. They lie across central Somerset like a gigantic backslash.
In the foot-hills of the southern-most slopes of the Mendips lies a city called Wells. The most widely known fact about the place - that it is the smallest city in England - is also the least interesting. The Mendips, however, contrary to their present vegetative and water-rich state, were once part of a vast mountainous desert region. 220 million years ago the Mendips of the Triassic period basked under a much more equatorial band of sunlight. Proto-dinosaurs populated its slopes. The over-riding colour of the desert was rust-red, due to a high iron content in the rock. This haematite still stains the soil of the fields, and turns the floodwaters a dark terracotta.
Later, and for a long period of time, they were the sea-bed of a long forgotten ocean. For millions of years they were underwater, collecting the bodies of countless generations of organisms which would later be turned into council houses. Then the waters receded and the hills were once again populated by land organisms. The water hadn't receded that far though, and the Mendips were now dressing themselves as tropical islands, fringed with sandy beaches and, a little further out to sea, banded by massive coral reefs. These islands were the breeding-grounds of icthyosaur and plesiosaur. The upland forests were patrolled by giant dragonflies, some of which sported wingspans of over 30cm.
Today, most of the Mendips have been eroded back to roughly the heights they reached during the Triassic period. The sand of the beaches that ringed the hills when they were tropical islands was sifted down through the sea, to be compressed into sandstone. The impressive scissor-arched cathedral at Wells is constructed of this material, and represents one of the most enduring sandcastles ever built by humans.