PELOPHILOUS FORMATION OF LEFT BANK OF SEVERN ESTUARY. 13 
be seen to fall and their vegetation gradually changes into that 
characteristic of the next lower level. Since I have been studying 
this coast vegetation, additional patches of brushwood and stones 
have been inserted here and there at the crumbling edge of a zone 
to stay this onward march of the tide. 
(4) In some places on the shore, for instance near Oldbury-on- 
Severn, the indications point to a small outer dune having been 
broken down by the tide, and as a consequence the vegetation 
of a strip of pasture land between the outer dune and an inner 
and stronger dune shows a tendency to go back to a more 
halophytic type. Such a tendency is undoubtedly retrogressive, 
and there is no doubt that the reclamation of this land and pasture 
by well built dunes is a comparatively recent process. 
A very characteristic feature of this gradual subsidence and 
disappearance of the formation, is the manner in which the level 
sinks in definite zones. Evidently, as the scouring action proceeds 
and the outer mud is carried away, great pieces of the inner 
vegetation sink together, so that the vegetation falls in a series 
of steps. The difference in level between these steps usually 
occurs quite suddenly, and may be either just a few inches or as 
much as five or six feet. This is a very striking feature of the 
whole formation, and a very interesting one, because these sharp 
changes in level are accompanied by very sharp changes in the 
vegetation. The different levels within the formation present will 
therefore be discussed when the plant associations are described. 
Another feature of the general nature of the formation is that, 
while the succession of plant associations that occur during the 
gradual disappearance of the vegetation stand out very clearly, 
but little can be said as to its method of construction ; nowhere in 
this area have I found any indication of the building-up of such 
a halophyte formation, as Moss describes as occurring near 
Highbridge, lower down the Severn on the same bank. 1 
Except in the uppermost zone outside the dune, a zone which 
is only present in a few places on this part of the coast, and which 
is so seldom submerged that its halophytic character is practically 
lost, the plants upon the whole of these zones belong unmistake- 
ably to the same general type. They are in nearly all cases low- 
growing herbs or small shrubs, either annual or perennial, only 
reaching a height of six inches to a foot on the open shore, even 
when grazing is prevented by local circumstances, but in places 
sheltered from the wind the flowering stalks of Aster Tripolmm, 
Triglochin maritimum, &c, considerably exceed this height (see 
p. 12). All these plants possess either succulent or very reduced 
leaves, the commoner character being succulent leaves with 
woody stems. 
1 Moss loc. cit. p. 18. 
