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.
Moors as a whole, being based upon a peat soil, are developed in regions that are humid, and it is natural that they occur most frequently in the uplands. But there are lowland moors also, which usually occur in association with estuaries or lakes, where they are formed above silt or alluvium or lacustrine mud. When there is much lime the first stage has been a bog.
The estuarine lowland moors are formed upon extensive beds of silt, as in North Lancashire, and are called Mosses, and occupied old filled-up upland valleys. Cotton Grasses, Tufted Bulrush, Ling, Cross-leaved Heath, Rosemary, Bog Mosses, Beak Sedge, Cranberry, Bog Asphodel, and Sundews are characteristic of these estuarine moors. In the lacustrine moors there are in the peat successive layers with Bog Mosses, Cotton Grasses, Prickly Twig Rush, Reed, Birch, Ling, etc. The valley moors of the New Forest show Bog Moss, Purple Moor Grass, Reed Swamp associations, and Alder thickets.
The upland moors lie on the slope of the hills, e.g. Pennines, between 1000 and 2000 ft., and in Scotland are found up to 3000 ft. They are distinctly drier, and trees are absent as in the original condition. The following associations occur: Bog Moss, Cotton Grass (1200-2200 ft.), Tufted Bulrush (1250-2000 ft.), Bilberry Moor (up to 3000 ft. in Scotland), Heather Moor (700 ft. or 1000 ft. to 2200 ft.). Elsewhere Rush societies and others of stagnant hollows occur. Grass Moor takes the place of these associations in some parts of Scotland.