154 TRANSACTIONS OF THE [Sess. LXXV. 
pseudacorus is also really a marsh plant, but owing to its 
deep rooting it may invade plains sufficiently high above 
the water-table for grasses to dominate. 
Sub-Formation II.—Neutral Meadow. 
Extremely local. What occurs may be regarded as a 
variety of marsh-meadow without sedges or as neutral 
pasture. This type is rich im species. See example 10. 
Sub-Formation IIT.—Calcareous Meadow. 
This, as mentioned previously, is a special type occurring 
locally, where there is much shell sand deposited by the 
wind. The effect of this constant supply of calcium car- 
bonate is to render the soil alkaline. The result is a very 
marked difference in the marsh vegetation in such areas 
from that of the ordinary type, the most striking being 
the practical absence of sedges. The characteristic sedges of 
the alkaline Fens of England do not occur in Orkney, or 
they might have been found here, but the soil is evidently 
not suited for the indigenous species. Hqwisetwm limosum 
is usually the dominant plant, with much Agrostis alba, 
and in passing to drier conditions the grass gradually 
assumes dominance. At higher levels other grasses appear 
and many marsh-meadow plants, but still as a rule no 
sedges. A Poa pratensis association was observed in one 
fairly dry place, but as a rule the meadow consists of little 
but Agrostis alba—with Hquisetum limoswm as it grades 
into marsh. To distinguish it we may call this :— 
1. The Agrostis-Equisetum limosum association. See 
examples 11 and 12. 
FoRMATION IJ.—Dry PASTURE. 
Grassland in which the bulk of the soil water is derived 
from precipitation and not added to by springs or drainage 
from elsewhere. 
The usual aspect of the vegetation is that of an even 
sward, starred, it may be, with flowers of dicotylous and 
monocotylous herbs, which do not, however, rise to any 
great height. The most characteristic are in fact of more 
