Over Crook Peak and Wavering Down

The rock which forms the Mendips, as well as the White Peak and the Yorkshire Dales, used to be known as the Mountain limestone. This name has sadly been abandoned - perhaps after complaints from the non-Mountain limestones of Everest, the Pyrenees and the Eiger? Now called Carboniferous limestone, it was laid down at a time when England was under water and drifting slowly north across the equator. The next rocks to form on top, as the Carboniferous sea became a swampy river-delta, were the coal measures. A thick layer of coal has in fact eroded off the top of the Mendips and, like the Pennines, the Mendips have a coal field next door.

In the Pennines the limestone is layered with waterproof gritstone so that dry ground alternates with peat bog. The Mendips are limestone all the way down. This gives a very enjoyable form of walking or (perhaps even better) horse-riding. The grass is cropped short by roe deer and rabbits, and bright in spring with lime-loving wild flowers. The sides drop away in hawthorn scrub and the mildest of craggy bits to a wide, fertile plain. The path along the ridge is fast and easy, and every 20 minutes it peeps down into another wooded hollow. The other side of Somerset, the Quantocks, are a different sort of limestone but give the same delightful walking. Sadly, the Quantocks and the Mendips are small in area. Furthermore, elsewhere in England, or even in the world, there isn't very much of this limestone downland at all.

Geologists believe that, oddly, this is the second time around for the Mendips. The continental collision nicknamed 'the Africa Crunch' folded the sea-bottom limestones into mountains of about Ben Nevis height (which isn't very high - Ben Nevis in its prime was Everest height). The soft, coal-like stuff was eroded away and the Mendip Mountains wore down to their present shape in the early dinosaur age. Then Britain sank, and the mountain outlines disappeared under thousands of feet (up to 1,000m) of ocean sediments. The next event, 'the Alpine Crunch', lifted everything up again about 50 million years ago, and since then the topping has gradually worn away to reveal the limestone landscape underneath.

According to this theory, the limestone gorges around the Mendips have formed twice over. The first time, as wadis or desert valleys scoured by flash floods; the second time, under Ice Age conditions, with the underground waterways frozen. Thus contradictory geological noticeboards explain Burrington Combe (desert wadi) and Cheddar Gorge (Ice Age meltwaters). Given that limestone gorges don't have rivers, they ought not to occur even once; doing it twice, for two different reasons, is good going!

While you're there

King John's Hunting Lodge is a half-timbered house at the centre of Axbridge. Although King John granted this attractive old town its charter, he died about 300 years too early to take advantage of his supposed hunting lodge: the building is actually the house of a prosperous 16th-century merchant. It's now the town's free museum.

Where to eat and drink

The White Hart at Cross has undeniable atmosphere. Some of the Bloody Assizes were held here after the Battle of Sedgemoor and the inn is haunted by the ghost of one of Judge Jeffreys' victims. Rather more substantial is the inn's home-cooked food.

What to look for

Limestone is made of snails - or at least of the calcareous hard parts of sea molluscs. Equally, snails are made of limestone, and flourish where calcium for shell-building is available. The shell is not only for protection from predators, but also keeps the snail from drying out. Accordingly, you are likely to see Crook Peak's snails in damp corners and on drizzly grey days. In these conditions you may be surprised at the brightness of snails - they are not just brown, but come in pinks and yellows as well.