354 MR FRANCIS J. LEWIS 



buried forest of the South of Scotland is wanting in the Hebrides, and its place is taken 

 by beds indicating moist insular conditions. This is what might be expected, — for dry 

 Continental (forest) conditions in the South and East of Britain would hardly extend to 

 those outlying portions in the West which were fully exposed to the influence of the 

 Atlantic. We should then have the interesting fact that, during a dry forest period 

 when the peat mosses over the greater part of Britain became clothed with pine 

 and Calluna, the type of flora associated with wet insular conditions continued to find 

 a refuge in the extreme West— only to flow out eastwards again on the destruction of 

 the forests and the resumption of insular conditions over Britain. 



The peat coming under the second heading has, so far, only been found in the 

 Eastern and Northern Highlands. The evidence here is much more conclusive, owing to 

 the presence of two well-marked datum lines. In Inverness-shire on the Spey- 

 Eindhorn watershed, at about 2000 feet, the series of events can be clearly traced, and 

 direct comparison made with the peat described from the South of Scotland (3). 



The peat here began to grow under Arctic conditions soon after the deposition 

 of the glacial deposits upon which it rests. Arctic willows (Salix reticulata and 

 S. herbacea) are dominant in the basal layers, gradually changing to a type of 

 flora indicative of sub-Arctic conditions (Salix Arbuscula, Betula nana, Empetrum 

 nigrum, Potentilla Comarum, etc.). After that, the flora changed ; the moors, 

 hitherto covered with shrubby sub-Arctic plants now bore a close growth of Eriophorum 

 and Sphagnum, amongst which a shrubby growth of birch managed to find a footing. 

 The humid conditions apparently became more pronounced, as the birch presently 

 disappeared, and vegetation was represented only by Sphagnum. Thereafter, Sphagnum 

 ceased to flourish, and a forest of pine with an undergrowth of Calluna overspread the 

 peat. G-unnar Andersson (5) has described the causes which, on some of the Swedish 

 peat mosses, lead to the alternation of forest formations and Sphagnum beds. Accord- 

 ing to this author, tree growth does not persist for any length of time upon Sphagnum 

 remains, the organic nutriment which has collected on the surface being soon exhausted, 

 so that the forest is weakened and invaded by a new growth of Sphagnum. Layer 

 upon layer of this plant is formed, until the land becomes so dry that heath formations 

 appear and contribute to further decomposition, paving the way for a new forest growth. 

 The replacement of Sphagnum by pine forest in the Scottish areas does not bear 

 evidence of having been caused by such changes in the food contents of the peat, 

 seeing that this upper forest of pine is, with one or two exceptions, alw r ays present in 

 the peat, whether it lies on steeply sloping or level ground, either at high or low 

 elevations. Further, the upper forest zone always occurs at the same horizon in the 

 peat, and gives place again to Sphagnum and Scirpus beds, which have persisted down 

 to the present time. If the phenomenon was due to the causes described by Gunnar 

 Andersson, one would expect to find different districts showing different alternations — 

 some more and others less frequent changes from Sphagnum moor to woodland. As it 

 is, districts so widely separated as Caithness-shire, Inverness-shire, and Galloway show 



