790 MR FRANCIS J. LEWIS 



with peaty debris, which, on examination, yields small pieces of birch bark and xylem 

 elements. Small birch twigs are occasionally met with in this layer. The stones and 

 boulders bear evidence of weathering, and the whole layer is strongly suggestive of an 

 old land- surface long exposed to subaerial denudation before the overlying peat began 

 to form. This passes downwards into compact boulder clay consisting of stiff, sandy 

 clay containing many large stones and boulders ; after the clay, which clings to them 

 closely, has been washed away, many of them are found to be strongly striated. So far 

 as I have seen, this succession is repeated in all the areas covered with the later growth 

 of peat that were examined in 1909. Particulars of individual sections will be given when 

 describing the several districts visited. The areas to be described are as follows : — 



(a) Walls district on the west of Shetland Mainland. 



(b) Weisdale and Voe in the centre of Shetland Mainland. 



(c) Island of Foula, 25 miles west of Shetland Mainland. 



(a) Walls. — This district is, perhaps, with the exception of the island of Yell, the 

 most extensive peat-covered area in Shetland. 



The general features have been described in a former paper (3). The newer series 

 of peat can be well seen owing to the great number of exposures made by the peat- 

 cutters on each side of the road between Walls and Sandness. In all cases only the 

 younger unstratified peat deposits have been cut, giving excellent exposures of the 

 weathered layers of upper boulder clay, but showing nothing of the older deposits with 

 the forest bed and two arctic plant beds. Indeed, it is not too much to say that anyone 

 examining the Shetland peat from the turbaries alone, without having sections cut in 

 the valleys and on the plateaux of the higher hills, would conclude that the deposits 

 only average 3 feet in thickness and are quite unstratified throughout. When the 

 deeper deposits are cut for fuel, the cuttings are not usually carried down as far as the 

 forest bed, so that the most careful examination of the district would not lead anyone 

 to suspect the existence of the deep stratified older peat. 



The newer peat resting on weathered boulder clay may be described first. An ex- 

 cellent section is exposed on the Sandness road about two miles north of Walls. This 

 section is shown in PI. II. fig. 3, and the stratification is as follows : — Depth of peat, 

 5 feet 8 inches. The upper layers consist chiefly of Sphagnum sp., Calluna vulgaris, 

 Scirpus csespitosus, Potentilla tormentilla, whilst towards the base Eriopiliorum 

 vaginatum becomes a characteristic feature. The lowest 2 or 3 inches which rests on 

 the weathered boulder clay is structureless, black in colour, and very hard, and has 

 the appearance of having been accumulated very slowly, so that the structure of the 

 plants has been entirely destroyed. 



This peat rests on a layer 12 inches thick of angular and partly rounded stones, with 

 the interspaces filled with clay strongly coloured with peaty debris. In some places the 

 clay contains a considerable amount of peat and numerous small fragments of birch bark 



* The nomenclature of Hooker's Student's British Flora, third edition, is followed throughout, except in certain 

 where the authority is given after the species. 



