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A monument in slate at the summit of Honister Pass (Stages 3A and 3B, and Route 8)

Some 400 million years ago the fells would have been of Himalayan proportions as violent volcanic activity pushed up from below to form a very high mountain range. But millions of years of erosion have reduced them to their present size, exposing igneous intrusions, which originally cooled and crystallised hundreds of metres below the surface. About 350 million years ago, most of the land sank beneath a warm tropical sea that teemed with life. The remains of these life forms created a thick layer of sediment made up of shells, fossils and coral all over the seabed, which eventually formed the pale grey Carboniferous limestone that runs around the perimeter of the national park. In other areas to the west, this sea was filled in with fertile mud and sand that resulted in the growth of forests, which decayed to form the belt of coal that was the lifeblood of heavy industry in West Cumbria.

During the last two million years, the Earth has gone through repeated periods of glaciations separated by warmer periods that supported the growth of broadleaved forests. It is the action of glaciers and the continual freezing and thawing of melt water during this period that has shaped the fells we know so well today. After the last period of glaciation, the sea levels changed and soils formed below the oak forests in the valleys. However, clearing the forests for cultivation in the 11th century led to some soil erosion and the formation of alluvial fans and lake deltas characteristic of the central and southern parts of the region.