142 C. E. Moss, W. M. Rankin and A. G. Tansley. 
coeruleum, Myosotis sylvatica, Campanula latifolia, Cardans hetero- 
phyllus , Hieracium spp. The lady’s slipper orchid ( Cypripedium 
Calceolus ) is extinct in Derbyshire, but it still lingers on in 
Yorkshire and Durham. 
A sh-Birchivood. 
In the limestone districts of the extreme north-west of England 
the woods of the ash series exhibit a considerable deviation from the 
type. While the differences scarcely affect the ground vegetation, 
the uppermost or tree-layer shows considerable modification. The ash 
is less abundant, and the birch ( Betula tomentosa) more abundant 
than in the typical ash-association; while the sessile-fruited oak 
(Quercus sessiliflora ) is also sometimes present. This is to be 
distinguished as the ash-birchwood, which is apparently conditioned 
by the climatic environment. 
These ash-birchwoods are not numerous, even in this district. 
They are found on the precipitous slopes of the narrow limestone 
valleys or dales, and particularly on the face of the Pennine 
escarpment. This rises almost vertically some 2,000 feet above 
the plain and looks westwards towards the hills of the Lake District; 
and against it the “helm” wind, peculiar to this type of land- 
relief, impinges violently. The exposure to both wind and radiation 
is extreme, and in marked contrast with that of the sheltered 
valleys of the south. The highest altitude attained by the ash- 
birch woods is 1,250 feet, and the local annual rainfall is about 50 
inches. 
At the higher levels the birch ( Betula tomentosa ) is practically 
pure, and with it is associated the mountain ash ( Pyrus Aucuparia). 
At lower levels the ash ( Fraxinus excelsior ) is abundant, accom¬ 
panied, as in the typical ash-association, by the wych elm ( Ulmiis 
montaiia ) and by Quercus sessiliflora. When such a wood is viewed 
in mass, the stout grey branches of the ash stand out prominently 
against the delicate brown tracery of the branches of the birch. 
Of shrubs, the hazel ( Corylus Avellana) is extremely abun¬ 
dant; the sallow (Salix caprcca), the holly ( Ilex Aquifolium) 
and the hawthorn ( Cratcegus monogyna ) are frequent; while the 
whitebeam ( Pyrus Aria), spindle tree ( Euonyntus europceus), 
buckthorn ( Rhaninus catharticus), dogwood ( Cornus sail guinea), 
and yew ( Taxus baccata) are absent except in South Lonsdale. It 
will be noticed that in their place are associates typical of the 
oakwoods. 
