720 MR FRANCIS J. LEWIS 
to any great growth of peat, yet, where it does occur, the amount of denudation to which 
it has been subjected is shght compared with the wasting away of the thick mantle of 
peat covering all the watersheds of the rivers Tees, Tyne, and Wear. 
An examination of the successive beds of vegetation contained in the older mosses 
shows that the rate of peat formation has not been uniform, for the length of time 
required to form a layer of closely-compressed stems of Empetrum and Arctic willows 
only a few inches in thickness, might possibly be sufficient to form several feet of 
Sphagnum peat. It would seem, then, that peat formation has been almost arrested 
at some stages in the history of the mosses; and I have met with features in the 
Merrick-Kells mosses which suggest that the peat has been subjected to denudation 
about the time of the formation of the Arctic plant-bed. 
SuMMARY AND GENERAL CONCLUSIONS. 
The peat in all the districts examined shows a definite stratification of plant remains, 
indicating a swing from woodland to heath and moss, and again to woodland. In some 
districts, an Arctic plant-bed is interposed between the lower and upper woodland beds. 
GuNNAR ANDERSSON has described alternations of woodland beds, with Sphagnum, 
and with heather layers, as occurring over large areas in Central and Southern Sweden, 
and he attributes such alternation to changes in drainage caused by the throwing up of 
a clay or sand bank by natural or artificial causes near a moss territory, thus causing 
flooding, and consequently favouring the growth of Sphagnum at the expense of wood- 
lands. This may quite possibly have produced like results in similar districts in Britain ; 
but in the hill districts described in the course of this paper such causes cannot have 
operated, as the mosses are situated on steeply-sloping ground on which no natural or 
artificial dam could be created. The regularity of the sequence of the beds, and their 
general agreement on similar although widely separated areas, tend to show that these 
beds represent successive changes in the vegetation which have been brought about by 
climatic changes at the passing away of the glacial period. 
None of the Scottish districts investigated by the author show any remains of Arctic 
plants at the base of the peat; but, on the contrary, some of them, such as the 25-feet 
raised beach mosses, contain remains of hazel in the basal layer. From the discovery by 
the late Mr James Bennie, of Arctic plants in the old alluvia of the Edinburgh district 
(14), the same features were expected at the base of some of the deeper lowland mosses, 
such as those in Wigtonshire. The presence of woodland at the base of these mosses, 
however, suggests that they did not originate until a temperate climate had replaced 
the Arctic conditions of the mer de glace period. In the Cross Fell peat, at 2500 
feet, a bed of Arctic willows and Empetrum has been met with lying on the clay at the 
base of the peat (15), and, on recently re-examining this bed, I was struck by its great 
similarity to the Arctic bed lying between the two woodland zones in the Merrick-Kells 
mosses. 
A summary has been given by Prof. Gurkig (16) of many of the more important 
