90 VEGETATION OF THE PEAK DISTRICT [cH. 
generally) below actual Alpine limits, are largely the result of 
the retrogression or decay of the original forests. 
Whilst this process of the lowering of the altitudinal 
forest limit in post-glacial times has, in my opinion, been 
essentially a natural process, it undoubtedly has in this, as in 
most localities, been greatly aided by the indiscriminate felling 
of trees by man and by the browsing of quadrupeds. 
BuRIED TIMBER IN THE PEAT 
The most direct evidence regarding the former greater 
development of forest in the district is to be derived from a 
study of peat deposits. The number of memoirs dealing with 
this subject is legion; and practically all the writers have 
emphasized the view that the deposition of peat, in a large 
number of instances, has been preceded by the occurrence of 
forest. Equal emphasis, however, must be placed on two 
other facts. First, forests may degenerate and still no peat 
deposits may occur on the site of them; for example, the 
degeneration of woods on chalk rock or on limestone or on steep 
shaly slopes is not succeeded by peat deposits. Secondly, peat 
deposits may be laid down without the occurrence of any pre- 
existing forest; for example, peat is now filling up some of the 
Cheshire and Shropshire meres and the Norfolk broads; and 
in these localities it is clear that the vegetation preceding the 
deposition of the peat was a reed swamp with no arboreal plants ; 
and also on the highest parts of the Pennine watersheds, peat 
may occur to the depth of twelve feet (363 cm.) or more without 
there being any trace of buried timber. 
During the course of this vegetation survey, many instances 
of buried timber have been recorded on the field maps. The 
general inferences to be drawn from the facts are that tree 
trunks occur at the base of the peat of several of the heather 
moors and the lower cotton-grass moors, but that on the highest 
moors buried timber is frequently absent. Generally, it may 
be said that remains of trees are found under the peat in the 
more sheltered parts of the moor and are absent from the most 
exposed places. The buried trees which have been noted 
consist almost wholly of birch (probably Betula pubescens); but 
aspen (Populus tremula), oak (probably Quercus sessiliflora), 
