156 TRANSACTIONS OF THE [ Sess. nxxV. 
Sub-formation I1I.—Sand pasture. 
1. Festuca rubra association. 
Sub-formation [V.—Maritime pasture. 
1. Festuca rubra association. 
Sub-Formation I.—Heath Pasture. 
This type of formation is also termed grass heath, and 
grouped along with shrub heath, ete., regard being had 
chiefly for soil character. Laying more stress on the 
physiognomy of the vegetation, it may be permissible to 
include it with other grassland. 
It is not natural to Orkney. Only through repeated 
burning of the heather and long-continued pasturing of 
sheep or cattle has Calluna in a few places given way to 
Nardus or Agrostis. This has been most completely 
attained on a steep northern slope where direct sunshine 
is at a minimum, such as the north slope of Kierfea Hill, 
Rousay. 
A certain geological formation seems also to favour 
Nardus. <A certain section of the Rousay beds, character- 
ised by the formation of terraced hillsides, tends throughout 
its range in Westray, Rousay, and Evie to bear a heath 
with sub-dominant Nardus. 
Atfirst sight the practical absence of grass heath in Orkney 
seems remarkable, since most of the Feeroes is covered by 
it. Ostenfeld is inclined to lay more stress on the insular 
climate than on the geological factor—the basaltic rock—as 
the cause of the great development of “ grass-moor” in the 
Feroes; but, having regard to the distribution of heath 
pasture and Calluna heath in the Scottish Highlands, the 
ereat importance of the chemical nature of the rocks is 
apparent. There, as pointed out by Robert Smith, pasture 
occurs on the rich schists, and heath on poor sandstones, 
quartzites, etc. The arenaceous and argillaceous sedimen- 
tary rocks of the Orkneys bear a somewhat similar relation 
in chemical constitution to the basalts of the Feeroes, as 
do the two types above to one another. 
Ostenfeld’s association of Nardus along with Juncus 
squarrosus and Scirpus cespitosus as “grass moor” will 
be discussed further in treating of the “ moorlands.” 
