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.
Many causes have contributed to the disappearance of the wet-soil types of vegetation such as bogs and marshes. The moorlands, which are drier, and situated mainly above the zone of cultivation, have, however, largely escaped, and they are probably of far greater extent than the bog or fen type and marshes.
The fen type, since it is largely lowland, and developed upon soil which is valuable for agricultural purposes, has been most largely affected. But in spite of this there is a good deal of country in the original state of the Fens.
Bogs, lowland or upland, however, have been greatly reduced in extent. The lowland types now only survive in an altered condition, having by artificial agency been transformed into marsh or wet meadow. In some cases they are to be discovered only by a careful survey of the country yard by yard, or field by field. The same applies also in a great measure to heaths and similar vegetation developed upon peat or ground with stagnant water, liable to be removed. When wet peat is drained it may become a moor, or a wet or dry meadow or grass heath.
We have ventured to call such traces of former bog or heath "vestiges", since they are now merely an indication of natural vegetation almost obliterated. Marshes are similarly liable to become lost or completely altered by kindred causes.