This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Bogs and Moors.1 - Bog and moor both owe their origin to the clearing of forests from regions which became waterlogged, and thus established conditions suitable for the formation of peat. A fen resembles a bog, but includes marsh, with lowland vegetation, and contains very little peat. In the case of bogs and moors the peat is thick. They are developed upon the higher parts of the hilly tracts in the north and west; but a bog is essentially a wetter type of formation than a moor. Moors occupy in fact more convex portions of highlands than the bog or fen, which have a concave basis, or lie in hollows.
The moor also is similar in some respects to a heath in being drier, and the peat is the subsoil for similar types of Ericaceous plants. But the subsoil of the moors does not, as in the case of heaths, affect the vegetation, the sand and gravel underlying a heath with thin peat or humus being confined to particular districts. The moor and the bog or fen then are characteristic of the more humid parts of the British Isles.