111] SCRUB ASSOCIATIONS os 
alder (Alnus glutinosa), hazel (Corylus Avellana), mountain ash 
(Pyrus Aucuparia), and willows (probably chiefly S. cinerea) 
occur more or less rarely; and in one locality Scots pine (Pinus 
sylvestris) was found. 
The highest examples of buried timber consisted wholly of 
birch, and were encountered on the southern extremity of the 
plateau of the Peak at an altitude of nearly 1800 feet (549 m.); 
and generally it may be concluded that the buried timber 
proves that in former times trees ascended the southern 
Pennines about 200 feet (61 m.) or 250 feet (76 m.) higher 
than they do at the present time, that this ancient forest was 
composed principally of birches, and that more or less uncommon 
associates were the aspen, oak, the alder, the hazel, the mountain 
ash, the willow, and the Scots pine. 
DEGENERATION OF WOODLAND 
There can be no doubt that a certain amount of the 
degeneration of the woodland of this district has been brought 
about by the indiscriminate felling of trees, the absence of 
any definite system of replanting, and the grazing of quad- 
rupeds. It is doubtful, however, if these causes are quite 
sufficient to account for so great a lowering of the upper limit 
of forest as 250 feet (76 m.), and for so general a phenomenon. 
It must be remembered that the population of the remoter 
valleys, many of which are now treeless or almost so, is very 
small; and the district does not appear to have ever been a 
great grazing district. 
The inability of certain forests to rejuvenate per se has 
been pointed out by many foresters and plant geographers. 
In discussing the causes of the succession of forest to heath in 
north Germany, Krause (1892) emphasized the view that the 
narrowing of the forest area has been largely due to errors in 
sylviculture, especially to the grazing of cattle in the forest. 
That such a factor is a causa vera in the degeneration of forests 
is indisputable. Graebner (1901), on the other hand, lays stress 
on the gradual impoverishment of the soil caused by the removal 
of the tree trunks, by the gradual washing out by rain of the 
soluble mineral salts originally present in the soil, and the 
spreading of heath vegetation on the forest floor consequent 
