MICROPALH ONTOLOGY OF POSTGLACIAL DEPOSITS. 487 
B. 55 em. Eriophorum vaginatum peat; the upper 15 em. yellow-brown 
(H=4), with traces of Calluna ; the lower 40 em. dark brown ; H not 
reaching 6. 
C. 93cm. Sphagnum peat, not quite typical, H>6; remains of FE. vagi- 
natum and Calluna. 
D. Rock. 
A sample collected 130 cm. below the surface showed 1 Alnus, 2 Betula, 
and 2 Corylus pollen-grains ; and a sample of the bottom substance, 
160 em. below the surface, 8 Alnus, 16 Betula, 1:5 Pinus, 1 (2?) Quercus ; 
1 Corylus. In its pollen character the last sample, in which also 2 Polypo- 
dium spores were seen, resembles several of the bottom samples already 
mentioned, e.g. from Wideford Hill (p.483), Helmsdale (p.478), and 
Achnasheen (p. 456). 
Among the following peat mosses, the first is situated in the parish of 
Sandsting, near the Walls-Sandness district ; the others are in the middle 
of the mainland, between Weisdale in the south and Firths Voe in Delting 
in the north. 
Prat Moss No. 33. (Text-fig. 17.) 
A smooth meadow with drainage dykes, a little W. of Murraster, near the 
Bridge of Walls-Tresta road, about 20 m. above sea-level (a short description 
is given in Verh. d. int. Ver. Limnologie, Bd. ii. 1924). 
Sequence of layers :— 
A. 260 cm. Magnocaricetum peat, H 7-8; with Equisetum and Meny- 
anthes. 
D. 170 cm.  Gyttja, of various tints; at 290-310 em. below the surface 
it is yellow-white ; 310-360 cm. brownish, with numerous rootlets ; 
360-400 em. yellow ; 400-420 cm. greenish yellow ; 420-430 cm. 
greenish. 
C. Rock. 
This sequence shows a very low PF, which as to the gyttja is greater in 
the upper than in the lower part. The percentages for the six samples were 
calculated when an average of 25 pollen-grains had been counted. Three 
conclusions can, however, be easily arrived at :— 
1. The dominance of birch-pollen. 
2. The presence of pine-pollen also in the oldest layers. 
3. The pollen of alder, elm, and oak first appear when the upper gyttja- 
layers are sedimented. 
Hairs of (Ceratophyllum were found in sample 7, and the pollen of Myrio- 
phyllum alterniflorum attains an enormous frequency (up to 750 per cent.). 
Also pollen of another species of Myriophyllum was seen. 
