IV] GRASSLAND ASSOCIATIONS 123 



grassland is there the rule. In the west of Ireland, calcareous 

 heath is widespread on an extensive lowland plain of Carboni- 

 ferous Limestone in co. Clare (see The New Phytologist, 1908 : 

 259). The calcareous heaths of the present district are rather 

 meagrely developed ; but examples occur at the head of Monk's 

 dale north of Miller's dale, and at the east of Longstone Edge 

 north of Longstone. Other examples occur south and south- 

 east of Buxton. There is rather an important difference 

 between the limestone heaths of Somerset and those of the 

 Peak District : those of Somerset usually occur below 850 feet 

 (259 m.) and those of Derbyshire above 1000 feet (305 m.). 

 Correlated with this altitudinal difference, there is a consider- 

 able difference in the floristic composition of the two associations. 

 Whereas the limestone heaths of Somerset are characterized 

 by only some half-dozen heath-loving species (albeit these 

 are often very numerous as regards individuals) and a very 

 large number of lime-loving species, the limestone heaths of 

 Derbyshire are characterized by a small number of lime-loving 

 species (which, however, are abundant) and a large number of 

 humus-loving species. A Derbyshire botanist may obtain a 

 rough idea of a Somerset calcareous heath if he imagines his 

 grassy dale-slopes to possess all the numerous lime-loving 

 species which actually occur there, and to possess, in addition, 

 numerous and well-grown plants of ling or heather (Galluna 

 vulgaris), heath (Erica cinerea), gorse {Ulex spp.), and bracken 

 (Pteris aquilina). It is a factor of some importance also 

 that the calcareous heath of Somerset occurs on slopes which 

 are much less steep than those of the limestone dales of 

 the Peak District of Derbyshire. 



Graebner (1901) has also stated that Galluna may occur on 

 calcareous soils, not incidentally but in quantity. A mixture 

 of calcicole and calcifuge species on calcareous soils has been 

 described by Geze (1908 : 463 — 4), who also states that the 

 lime is frequently leached out of the superficial layers of soil. 



It was suggested in the previous chapter that the greater 

 percentage of lime on the soil of the steep calcareous slopes is 

 probably due to the upper layers in such places being in process 

 of slow but continuous denudation ; and hence the superficial 

 soil is constantly changing, and new and more highly calcareous 

 layers brought into use for the plants. On the other hand, the 



