INTRODUCTION 87 



peat up to 30 ft., usually at higher elevations. They 

 include the following associations : Bog moss associa- 

 Hon, Cottongrass association, with a peat bed of four 

 layers. A third association is formed by Scirpns 

 ccespitosns, with Ling, Cottongrass, Sundew, Cow- 

 berry, etc. (see Fig. 21). 



The Bilberry moor association is dominated by 

 Whortleberry, and is rather variable in the com- 

 ponent species, due to the type of habitat. The 

 Heather moor association is characterised by Ling, on 

 dry peat with remains of Birch. The following 

 are typical plants : Dwarf Furze, Heath Bedstraw, 

 Bell Heather, J uncus squarrosns, Bent Grass, 

 Bracken ; and here and there the Whortleberry 

 becomes abundant. Rush societies and others 

 formed in damp hollows are also found in the same 

 habitats. 



On boulder clays a grass moor occurs between 

 the Scirpus ccespitosus association and siliceous grass- 

 land. Grasses, rushes, sedges, are characteristic. 

 Purple Moor Grass and Mat Grass are abundant. 

 Distinct associations are formed by each with 

 characteristic species. 



Above 2000 ft. there is arctic-alpine vegetation,* 

 which is found in Scotland^ as on Ben Lawers, and 

 on the higher hills and mountains of England and 

 Wales. Several zones are recognised, such as the 

 zone of cultivation and pasture, the latter above the 

 former as a rule and less altered. Above these comes a 



* This has been studied especially by Mr. W. G. Smith. 



