a chain of mountains in Great Britain. The Pennine Mountains extend for 250 km and have elevations to 893 m (Cross Fell). They are composed primarily of limestones and sandstones. The summits have plateau-like surfaces. The western slopes are steeper than the eastern ones. There are heaths, peat bogs, and meadows, while open woodlands (oak, hornbeam, and birch) are found in the lower zone. Tourism is important.