ON THE PLANT REMAINS OF THE SCOTTISH PEAT MOSSES. 803 



The layer containing these plants rested directly upon drift, and the lower true 

 arctic zones of the pre-forestian peat were wanting. 



(b) Weisdale and Voe. — The general features of a part of this district have been 

 described in a former paper (3). From Weisdale Voe a long ridge runs northward for 

 9 miles to Voe, for the greater distance at an elevation of 700-800 feet. Peat 

 covers the summits and flanks of the hills and the floor of the valleys on each side of the 

 ridge, ranging from 4 to 15 feet in depth. Above the 600-feet contour line the ground 

 is chiefly covered with Eriophorum, Sphagnum, and Empetrum. Almost the only 

 plants found here are : — Eriophorum vaginatum, E. polystachion, Sphagnum sps., 

 Scirpus cwspitosus, Empetrum' nigrum, Rhacomitrium lanuginosum, Calluna vulgaris 

 (stunted and scanty), Vaccinium Myrtillus ; and the general aspect of these moors 

 resembles the Eriophorum and Sphagnum areas on the Pennine Chain in Yorkshire and 

 Westmorland (5), except that Rhacomitrium does not form any characteristic feature 

 in the vegetation in the English district. Below 600 feet the slopes are covered with 

 Calluna moor and occasional patches of Eriophorum polystachion and Rhacomitrium 

 lanuginosum. Above 600 feet peat formation is still going on, although near the 

 summits wind plays a great part in denudation. Below this level denudation is going 

 on more rapidly, although not nearly so fast as in the Walls district. 



The summit vegetation above 600 feet is similar to that at about the same level in 

 Foula, and its distinctly more hygrophilous character may be due to the cloud-belt 

 which frequently and for long periods lies about 600 or 700 feet above sea-level. 

 Sandness Hill in Walls district rises to 817 feet, and here the same type is met with, 

 although it is not developed to the same extent as in Foula and Weisdale. 



As at high elevations farther west, wind appears to be the dominant factor in 

 causing denudation near the summits of the hills. On the summit of Weisdale Hill the 

 original covering of peat has been carried away by the wind, leaving the rock exposed, 

 except in one place, where a cap about 5 or 6 feet in thickness with steep bare sides still 

 remains. The same features are repeated on the summit of Scalla Field (921 feet), 

 Gruti Field, Marrofield, Fielnadringa and Sneugie, all about the same altitude. 



It is very difficult to see how the thick, continuous cap of peat which once covered 

 these very exposed summits could have been formed if the meteorological conditions 

 were similar to the present. 



In some of the valleys, large peat areas are being denuded owing to totally different 

 causes. Between the East Hill of Burrafirth and Bratta Field there is a long narrow 

 valley in which rises the Burn of Voxter flowing north, and a tributary of the Burn of 

 Marrofield water flowing south. The watershed is a slight plateau less than half a mile 

 across, and only rises a few feet above the rest of the valley. The southern part of 

 the plateau is curiously channelled and hummocked, so that it is a conspicuous object 

 some miles away. This is caused by the expansion of the southward-flowing stream on 

 the flat watershed. A flat expanse of deep peat has been overflowed by the burn, the 

 vegetation lying in slight hollows has been killed, leaving a flat expanse of bare peat 



