124 Plant-formation of 8iliceous Soils 



humus present in the soil may be roughly gauged by 



the abundance of such plants as the heather (Galluna 



vulgaris), the bilberry (Vaccinium Myrtillus), and the 



silver hair-grass (Desohampsia fiexuosa) in the ground 



flora. The soils are shallow, sometimes very shallow; and 



on the whole, therefore, the trees are of small dimensions. 



The Quercetum sessiliflor^ ascends, in general, to 



about 1000 feet (305 m.); and, above this 



level, the influence of altitude is seen in 



range. ' 



the absence of well-developed oakwoods. 

 Derivative scrub occurs, however, as well as small patches 

 of woods of Betula tomentosa, above this height. Birch- 

 woods are more extensively and typically developed in 

 the Lake District, and especially in Scotland, than on the 

 southern Pennines. 



The woods of Quercus sessiliflora have been described 

 by several writers^, and variously subdivided 

 character ™*° upland and lowland oakwoods, dry oak- 



woods, and mixed deciduous woods, etc. In 

 the present account, the woods described by these writers 

 are regarded as particular cases of the association of 

 Quercus sessiliflora. 



In all these woods, this species (Q. sessiliflora) is 

 indisputably the dominant tree. On the lower, non- 

 calcareous Pennine slopes, this species grows well and 

 forms fairly large trees on the damper soils up to about 

 800 feet (244 m.), especially on the shales: above this 

 altitude, especially on soils over the sandstones, the trees 

 are usually of short stature and small girth; and near 

 their upper altitudinal limit, they are Little taller than 

 shrubs. 



The pedunculate oak (Q. Bohur) is totally absent from 

 the great majority of the oakwoods of the 

 Pennine slopes, although it occurs here and 



' Smith and Moss, 1903 ; Smith and Eankin, 1903 ; Crump, Flora of 

 Halifax, 1901 ; Woodhead, 1906 ; and Moss, 1911. 



