How was Cheddar Gorge made?

Cheddar Gorge was made millions of years ago - amazingly enough, it began as a tropical reef. Fish bones, shells and other debris was deposited on the sea floor and because it was so deep down in the ocean, these sediments compressed, forming a sedimentary rock called limestone. Over many, many more years, the plates on either side moved inwards together, folding the sediments on the sea bed. During the ice age, glacial water froze in the cracks in the limestone. This made the rock impermeable - allowing water to flow over the top of it. As ice nearer the top melted, it carved into the ice and formed a river, but the ice underneath that was deeper down remained frozen. The water scraped away and eroded the rock and ice to create a valley as underground, the ice was still frozen. As the climate warmed, the ice deeper down melted, and the limestone became permeable. The river flowed underground, carving caves. The slightly acidic rain reacted with the alkaline limestone and dissolved it, and caves are still being created today. The water disappeared underground, and Cheddar Gorge remains a dry valley to this day.