Owing to the necessity for the development of peat on a large scale and the dependence on more or less moist conditions, bogs and moors are not widely dispersed in the British Isles; and indeed the plants which are characteristic of these types of formation are of very rare occurrence for the most part. This is partly due to the universal cultivation and drainage of the country after the cutting down of trees. But it is also due to more natural causes. These are the requirement of a considerable altitude, and the constant replenishment of the peat, which is normally developed only in regions of great rainfall.

1 See also Section IX, where dry moors are treated with heaths. The two divisions overlap to some extent.

Bogs and moors are, in fact, confined to the lofty mountains or hilly regions which are based upon the distribution of the older rocks in this country. These are found for the most part in the west of England, in Wales, in the Lake District, and in Scotland generally. Yorkshire also is mainly composed of lofty hills, covered by moorland vegetation. In Ireland peat is widespread in the whole of the northwest, and along the western half of the country. Thus moorland and fen are developed in the regions of the greatest rainfall and altitude.