ON THE PLANT REMAINS OF THE SCOTTISH PEAT MOSSES. 797 



and small pieces of twigs or roots, which are often mere tubes of bark, the wood having 

 disappeared. The clay containing peat has been examined, and contains very small 

 fragments and flakes of bark, stone cells similar to those found in the cortex of the 

 birch, and numerous xylem elements, vessels, tyracheids, and medullary ray cells. No 

 seeds or plankton have been found. The distinguishing features of this layer are : 

 the abundance of angular or subangular stones of moderate size showing traces of atmos- 

 pheric action, and the presence of peaty debris amongst the accompanying clay. The 

 junction of the peat and the altered boulder clay containing humus is shown in PI. II. 

 fig. 3. Unaltered boulder clay is encountered immediately be!ow, the transition being 

 accomplished in 2 or 3 inches. The characteristics of the boulder clay differ entirely 

 from the overlying layer. It is much more consolidated, the stones show no signs of 

 weathering and show fresh striated surfaces, and the accompanying clay and sand cling 

 so firmly that it is necessary to wash the stones for some time before a clean surface can 

 be obtained, whereas the clay and sand easily crumble away from the surface of the 

 stones in the weathered layer. These features are repeated in another roadside'' quarry 

 two miles nearer Sandness, in several sections on the road between Walls and Tresta, 

 on the Reawick road, and in numerous other sections throughout the district. About 

 fourteen sections were examined in which 3 to 4 feet of drift underlying the newer peat 

 had been exposed, and every one showed the essential features of the section first 

 described. One section near Reawick may be described, as, in addition to the features 

 given above, a well-developed iron-pan was found in the drift. 



The depth of peat was 3 feet 9 inches, and it rested upon 8-14 inches of weathered 

 material containing much peaty debris. This is often in faintly defined bands, and is not 

 composed of rootlets from the peat above, but of humus intimately mixed with the sand 

 and clay. Below this is an iron-pan about 1 inch in thickness which rests upon the 

 unaltered boulder clay, which here is exposed to a depth of 4 feet. A second iron-pan 

 is present in some parts of the section 12 inches below the first, but, unlike that, is not 

 continuous. At the base of the peat, resting on the weathered drift, are numerous 

 flakes of birch bark, and similar material is also found in the humus occurring in the 

 weathered drift. 



A section near Eela Water in the granitic region of the north of Shetland Mainland 

 showed the same features. This section is illustrated in fig. 1. 



If the phenomena were confined to a few spots, the view might be held that the 

 12 inches of stony material on the top of the unaltered boulder clay represented a 

 deposit near the edge of the receding glacier, where sub-glacial streams carried away 

 much of the finer material, leaving the heavier stones behiud. Its occurrence is, how- 

 ever, so general, both on level and steeply sloping ground, that T think this view is 

 untenable. The presence of birch debris not only on the surface but amongst the humus 

 in the sand and clay filling the interstices between the stones proves, I think, that a 

 considerable period elapsed between the deposition of the glacial drift and the formation 

 of the newer peat. The view is taken here that the 12 inches of stony material on the 



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