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 sesdlifiora), 



