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.
As intimated in Section XII, there are two altitudes at which Ling and Heath, or the chief components of a heath, occur. Though these two levels are not uniform, they serve to indicate the particular zones at which the heaths in different areas are found.
The English heaths of the South of England and the East Counties are more or less of the lowland type, and the same may be said of the Irish heaths, excluding the west coast moors and heaths. Of this type are Exmoor, Dartmoor, and numerous heath-clad commons.
Such heaths normally occur between 300 and 500 ft. above sea-level, but many of them come right down to the sea.
The upland heaths are developed in the hilliest parts of the country in the west, Wales, Gloucestershire, the Pennines, Lake District, Yorkshire, Scotland. They go by the name of moors in many districts, especially in Yorkshire. The height to which Calluna and Erica extend, respectively, differs, and upon this fact zones have been based. Ling ascends the highest (2000 ft.), and the Cross-leaved Heath next, Purple Heath the least of the three.