Folds

Folds result from the slow deformation of rocks. This happens deep underground where the rocks are under pressure and temperatures are higher.
Folded rocks are common in mountain ranges like the Alps, Himalayas and the Scottish Highlands.

Up-folds are called anticlines. The photo (below right) shows Sheep Mountain in the USA. This is how the Mendip Hills in Somerset (left) might have looked about 200 million years ago.

 
Down-folds are called synclines. The summit area of Snowdon is an example (see photo 3).

In a syncline, the youngest rocks (on top) are found in the middle of the fold – in an anticline, the oldest rocks (those underneath) are exposed in the middle.

View images of folding in Britain.