A Somerset Heath and its Bryophytic Zonation. 8i 
islands is formed (Figs. 1-3). The tussocks vary from a few centi¬ 
metres across to more than a metre, the height varying from a few 
centimetres to a half-metre in extreme cases; while the furrows 
separating them are intermittent or continuous channels of water, 
and in the latter case may be 50 cm. wide and deepened by erosion, 
but the ultimate ones are usually less than 15 cm. in breadth, and 
Kcao Road 
Fig. 1. Diagrammatic sketch-map of the heath. The furrows between 
the Molinia tussocks are represented by dotted lines, the size of the tussocks 
being exaggerated. The lowest portion of the heath is shown by the contour¬ 
line marked 0, the actual height above sea-level being approximately 350 feet 
(106 metres) ; the other contour lines indicate the increase in height in feet 
from this zero line. The stream and its tributaries are indicated by continuous 
lines. The road by the side of the heath is bounded by hedges which are 
represented by crossed lines. Scale 1 in 1000. 
are often very shallow. During wet weather the whole field is very 
wet, but after a period of drought the Molinia tussocks become dry 
and are separated by damp furrows. Under ordinary moist climatic 
