MICROPALZONTOLOGY OF POSTGLACIAL DEPOSITS. 479 
Calluna was the dominant plant, then followed Empetrum, Erica Tetraliw, 
Juncus squarrosus, Potentilla Tormentilla, ete. 
Text-figure 16 (No. 22) shows that the formation of peat began con- 
siderably later than the period represented by the A-zone, already mentioned 
many times. The lower half of the sequence is richer in pollen-grains than 
the upper. On an average there are 51 pollen-grains per sq. cm., exactly 
the same number as from the samples of sedentary material from Skye 
(ef. p. 465). 
In moss No. 23 (300 m. from No. 22) a series was collected from a peat- 
pillar about 75 cm. high, which had been isolated by erosion. The formation 
of peat probably began here at about the same time as in No. 22, as indicated 
by the analysis of the lowest sample : Alnus 29 per cent., Betula 47 per 
cent., Pinus 20 per cent, Quercus 3°2 per cent., Tilia 08 per cent. ; 
Corylus 4 per cent. 
E. Peat Mosses on the Orkney Islands. 
(Map used: Bartholomew’s “ Half-inch to mile " map of Scotland, Sheet 28.) 
The Orkneys are not nearly so rich in peat as are the Hebrides or Shetlands ; 
nevertheless they show several points of interest, especially when the 
Shetland Isles are compared with the nearest part of the Scottish mainland 
(Caithness ; neighbourhood of Cape Wrath). Lewis has published no 
descriptions of peat deposits from these islands. 
Peat Moss No. 24. 
This moss may be cited as an example of the distinct regenerative structure 
(ef. Sernander, 1910) sometimes met with in Sphagnum peat in Scotland. 
It is situated S.S.E. of Kirkwall, half-way between White Moss and Mark 
Stone Moss, about 60 m. above sea-level. The surface was clothed with 
a Callunetum. Solitary Rumex Acetosella also occurred. 
Sequence of layers :— 
A. 2Lem. Calluna peat, dark and dry ; a large number of Calluna stems 
and rootlets; no fibres of Æriophorum vaginatum. 
B. 3em. Sphagnum peat, bright brown, H<6; rootlets and fibres of 
E. vaginatum. 
C. 4cm. Peat, closely resembling layer A. 
D. 5cm. Eriophorum vaginatum peat ; no distinct boundary between this 
and 
E. 3 cm. Sphagnum peat (as B). 
F. 5 cm. Do., but dark, well humified. 
G. 6cm. Do., bright, only a little decayed. 
H. 8cm. Do., with a great quantity of very robust Calluna stems. 
LINN, JOURN.—BOTANY, VOL, XLVI. 2N 
