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.
The heaths of the British Islands occupy certain well-defined areas, where there is a considerable rainfall, on more or less sandy or gravelly soils. Thus they occur in the south and west of England, and in Scotland, and in the Midlands, and elsewhere on a lesser scale. The rainfall in Scotland, which may amount to 40 or more inches of rain annually, exceeds that in the English areas named by at least 15 in.
The heaths of the Eastern Counties have not more than 25 in. of rain per annum, and peat is not formed to any great extent. In the south of England it is much less. In Norfolk and Suffolk the Ling-covered areas may be transitional to grass heath, and also develop the flora of the chalk pasture.
In the Cornish area the Cornish Heath, Dwarf Furze, Ciliate Heath are characteristic. In the Midlands the heaths are ill developed. Yorkshire has great regions of heather, called moors. There is 35 in. of rain per annum, and both wet and dry heaths occur.