336 MR FRANCIS J. LEWIS 



flora. The older peat deposits in Scotland date back to late glacial times. They con- 

 sist entirely of plant remains, often stratified in the clearest manner, and yield evidence 

 of great changes in the distribution of the flora. 



The objects of the present investigation are, then, twofold : — (a) to obtain evidence of 

 the changes in distribution which have taken place since the introduction of the present 

 British flora, and (b) from those changes to reconstruct the main climatic fluctuations 

 marking the later stages of the glacial epoch. That the peat mosses will yield 

 abundant evidence on these points may be expected from the results already obtained. 



It is important to bear in mind that in dealing with plant remains in peat mosses 

 only certain plants are likely to be found — namely, those which either always or 

 occasionally grow on humus. In addition to these, a few seeds of plants growing on the 

 surrounding non-humus-covered ground will probably have been introduced to the peat 

 areas by the agency of animals or wind. 



It is only the greater and more widespread changes in vegetation whose records 

 occur in the peat ; many smaller fluctuations, due to modifications of local drainage or 

 alterations in the chemical character of the peat over certain areas, would hardly be 

 pronounced enough to persist for sufficient time to leave any definite record. One of 

 the most important points to be determined is whether the stratification met with is 

 local in character, or whether it occurs over a wider area ? It thus becomes desirable to 

 make a systematic examination of all the peat, taking it district by district. For the 

 purpose of comparing the peat strata in widely separated districts, two well-marked 

 datum lines are available — viz. the lower and upper buried forests. That these represent 

 widespread and considerable changes in the conditions is shown by their occurrence 

 wherever the peat is examined. Where such a buried forest is not found — owing either 

 to the elevation or the slope of the ground not having been favourable to tree-growth — 

 it is represented by a bed of dry humus-loving plant debris, which shows that dry 

 conditions prevailed generally during the period of forest growth. 



Method of Survey. — The same general method of procedure for examining the peat 

 deposits in the field and specimen blocks in the laboratory has been . followed on this 

 occasion as described in the paper dealing with the South of Scotland (3). The deposits 

 investigated in the North usually lie some distance from any areas of turbaries, and all 

 the deposits have been undisturbed by human agency since their deposition. As 

 sections yield much fuller evidence than borings, they have been made wherever 

 possible. Borings have only been resorted to on the Skye mosses, for, owing to their 

 flat, unbroken character, wet condition, and depth, section-cutting is difficult. The 

 evidence gathered from that region, however, does not rest entirely upon borings, for 

 many sections were made at different points ; borings were only used to obtain evidence 

 of the continuity of the beds found in the sections. So closely are these mosses 

 covered with vegetation that it is often a matter of some difficulty to cut through the 

 thick mat of vegetation to the underlying peat. 



The following areas are described in this paper : — 



