66 VEGETATION OF THE PEAK DISTRICT [CH. 
type, and to the association of ash-birch woods (cf. p. 40). In 
Somerset (Moss, 1907: 41), ash woods are well developed on 
the slopes of hills of Carboniferous Limestone, of the Dolomitic 
Conglomerate, and of the Jurassic limestones. The “oak-hazel 
woods” of Somerset (Moss, 1907: 51) also are to be regarded as 
conforming to the general ash wood type (see Watson, 1909; 
and Moss, Rankin, and Tansley, 1910: 138). “Oak-hazel 
woods,” 7.e., woods with oak standards and much hazel coppice, 
are of very general occurrence throughout southern England. 
Some of them have been derived from oak (Quercus Robur) 
woods, and others from ash-oak woods. The “oak-hazel woods” 
of Somerset must be referred to the latter class, because they 
contain among the coppiced layer a great deal of ash, which 
would spring up as standard trees if not coppiced, and because 
their “ground flora resembles the more shady portions of the 
ash wood” (Moss 1907: 52). 
In the Peak District, typical ash woods occur on the slopes 
of the hills of the Carboniferous or Mountain Limestone (see 
figures 9, 10 and 17). None is represented in the northern 
area, as there no limestone rocks occur. In the southern 
area, they are well represented, especially in Wye dale and 
Lathkill dale. 
The Carboniferous Limestone rocks of north Derbyshire form 
a plateau which attains a height of about 1550 feet (472 m.), 
and whose average height is perhaps 1200 feet (366 m.). The 
plateau is dissected by numerous valleys or “dales,” most of 
which are streamless. The limestone dales of the Pennines are 
comparable with the gorges and coombes of the Mendip Hills 
of Somerset, both from the standpoint of the geology and that 
of the vegetation. The dales of Derbyshire descend from the 
plateau, and the ash woods begin to appear on the slopes at an 
altitude of about 1000 feet (305 m.), above which altitude scrub 
occurs, but no genuine woods. The woods continue to the 
bottoms of the dales, which here descend to about 250 feet 
(76 m.). This is much lower than any of the ash woods 
or scrub on the Carboniferous Limestones of the mid-Pennines ; 
and, as in Somerset, the lower altitude permits of a better 
development of the dominant tree and the more characteristic 
shrubs and ground species of the ash woods. 
It. is probable that at some past time, the whole of the 
