vi] MARSH AND AQUATIC ASSOCIATIONS 147 
heather association or in the cotton-grass association: in the 
latter case, they occur in associations either of siliceous grass- 
land, scrub, oak or birch wood. In all cases, however, the 
source 1s marked by a swamp; and these swamps are frequently, 
but by no means invariably, dominated by the common rush 
(Juncus effusus). 
As might be inferred from the diverse surroundings of 
these springs, there is a certain amount of diversity in their 
flora. This difference, however, is less than might have been 
anticipated, as the springs are all characterized by some trickle 
of water implying a fair degree of aération, and all are character- 
ized by a low mineral-content, as is sufficiently indicated in the 
analyses just given. 
The poorest flora is found in the swamps surrounding the 
springs which occur on the peat moors. It is sometimes stated 
that the larger rushes do not occur on peat; but Pethybridge 
and Praeger (1905: 171) find an association Juncus effusus on 
peaty soils, and this is also the case on the Pennines; so that 
the statement is too sweeping. It is true that Juncus effusus 
is not a normal member of any of the plant associations on 
peat with stagnant water; but whenever water from a spring 
oozes through the peaty soil, there a community of the common 
rush frequently occurs. The springs change their positions 
from time to time, as may be seen by comparing the present 
springs with those marked on the old “six-inch” Ordnance 
maps. Probably when the peat was being originally formed, 
the land round the then springs would be destitute of peat; 
but when a spring at some later time issued from a different 
place, two local changes in the vegetation would be called into 
being. First, the swamp plants of the original spring would, 
after a time, die; and their places would be filled by plants 
from the neighbouring moorland association, arid peat would 
thus form on the site of the old spring; and secondly the 
aérated waters of the new spring trickling through the peat 
at a different place would result in the death of many of the 
moorland species of that place, and in the invasion of some 
swamp-inhabiting species. 
On the non-peaty slopes and at lower altitudes, the swamps 
are more numerous and much richer in species. However, the 
characteristic feature of all of them, whether on peat or not, is 
10—2 
