34 MR FRANCIS J. LEWIS 



evidence of interest both to botany and geology. On the one hand, it will give the facirs 

 of the vegetation which has during successive periods covered the peat mosses ; and on 

 the other, much may be learnt of the climatic conditions from the presence of certain 

 sets of characteristic plants in the strata. 



The work of the last three years has shown that many of our peat mosses began 

 their growth under arctic conditions, and thus, during some stage of the glacial period. 

 The successive strata in such areas will then contain the salient features of the types 

 of vegetation which have existed from that time down to the present. Direct palseonto- 

 logical evidence will then be available for a long period of time during which, geologists 

 are agreed, many climatic changes have occurred, though the amplitude of such changes 

 is still a matter of controversy. Differences in climatic conditions of small amplitude 

 would certainly affect the character and distribution of vegetation to a greater degree 

 than the alluvial drifts which were deposited whilst those changes were in progress. 



Before giving a detailed description of the deposits examined during the field work 

 in 1906 it may be well to review briefly the results obtained in 1904 and 1905. 



During the examination of large areas of peat it is found that certain datum lines 

 make their appearance in all the districts. The most prominent datum lines are two 

 beds of buried forest separated by a considerable thickness of intervening peat which is 

 always free from tree remains. These two forest beds — the lower and the upper buried 

 forest — are found in all large and deep peat mosses above 100 feet altitude which 

 have been examined in the south of Scotland. The lower forest consists of birch, hazel, 

 and alder ; the upper generally of pine. These forest remains are so well marked, and 

 persist over so wide an area, and are underlaid and overlaid by such closely similar strata 

 in the different districts, that there can be no doubt they represent true horizons. 



The upland valley deposits of the south of Scotland show a bed of peat containing 

 the remains of an arctic flora between the lower and upper forest bed. This is considered 

 to indicate a decided change in conditions between the dying away of the lower forest 

 and the appearance of the upper forest. Those peat areas below 300 feet, and near the 

 sea in Kirkcudbrightshire and Wigtownshire, contain beds of swamp vegetation between 

 the two forest beds instead of arctic plants, but these swamp plants are such that attain 

 a high latitude in Europe and Asia. In the south of Scotland the peat thus shows 

 a transition from a forest vegetation to one characteristic of Arctic regions, and this 

 gradually gives place to a second forest vegetation, which in turn is displaced by 

 bog and moorland vegetation persisting to the present time. 



The Highland areas so far investigated reproduce the later stages found in the 

 Southern Uplands, but the earlier beds are wanting. The basal layers of the peat 

 contain the remains of an arctic vegetation similar to that met with between the two 

 forest beds in the south. Above this, lies the upper peat bog covered with the upper 

 forest and recent peat. The upper forest consists of two distinct zones separated 

 by 1-3 feet of Sphagnum peat quite free from traces of wood. This is a feature of 

 constant occurrence in the Highlands, but it has not been found in the south of Scotland. 



