46 VEGETATION OF THE PEAK DISTRICT [CH. 



stable association occurs in which the two species are present 

 in almost equal proportions. Such transitional woods may 

 occur in localities where the two associations come into close 

 propinquity, and also sometimes on dry sandy or gravelly 

 soils. In such transitional woods, the hybrid oak (Quercus 

 Robur x sessiliflora) invariably occurs. The occurrence of this 

 hybrid, though quite general in such situations, was unsuspected, 

 so far as this country is concerned, until quite recently (see 

 Moss, 1910 a: 34). 



OAK WOODS OF QUERCUS SESSILIFLORA 



Woods of Quercus sessiliflora occur on the damp, shallow, 

 siliceous soils of the Coal-measures, the Millstone Grit, and the 

 Pendleside (or Yoredale) rocks, up to an altitude of about 

 1000 feet (305 m.). The rocks of the Coal-measure series, as 

 a rule, occur at moderately low altitudes, flanking the Pennine 

 watershed. On these rocks, the woods, whilst mainly confined 

 to the slopes of the hills, occasionally extend some little distance 

 on to the plateaux, whereas on the rocks of the Millstone Grit 

 and the Pendleside series, the woods are almost entirely confined 

 to the steep slopes of the narrow valleys or " cloughs " ; and it 

 is only rarely that they spread out on to the flatter and more 

 exposed plateaux. 



The woods of Quercus sessiliflora of the southern Pennines 

 have been described by previous writers. Crump (1904: xxxiii) 

 subdivided them into (a) mixed deciduous woods, and (6) dry 

 oak woods on the Coal-measure, Millstone Grit, and Yoredale 

 (or Pendleside) rocks. Smith and Moss (1903 : 387) and Smith 

 and Rankin (1903 : 159) adopted almost the same subdivisions 

 when they described (a) lowland oak woods and (6) upland 

 oak woods. Woodhead (1906), in describing their ground 

 vegetation, referred to them as (a) mixed deciduous woods 

 of the Coal-measure area (p. 336), and (6) mixed deciduous 

 woods of the Millstone Grit area (p. 347). However, all these 

 subdivisions are only particular aspects of the association of 

 Quercus sessiliflora as developed on shallow, siliceous soils. 

 The " pine woods " of Smith and Rankin (loc. cit.) are merely 

 plantations of conifers, on sites previously occupied by woodland, 

 grassland, or farmland. 



