94 
F. XV. Oliver. 
attach any quantitative (time) significance to the presence of a given 
lichen on a stone. From this point of view the lichens of the 
shingle hank are an untouched and highly promising field. 
Good indicator plants are also provided by the Angiosperms : 
thus Geranium robertianum v. purpnreum belongs essentially to 
dormant areas, whilst Lathyvus maritimus at its best is indicative of 
the unstable condition. 1 
The terrace or fringe is the great gathering ground of the 
halophytic plants—escapes from the salt-marsh. Other plants are 
those common to the back, especially on the dormant parts. 
Matricarias perhaps are characteristic. Lichens occur in great 
profusion and luxuriance, and include Cladonias and other fruticose 
and foliose forms. On the mobile places (detrital fans) Suceda 
fruticosa breeds and establishes itself: elsewhere it merely survives. 
This plant is the chief glory of those banks on which it occurs and 
offers many problems requiring explanation (cf. p. 92, footnote). 
Climatically, the terrace is warm and sheltered, in marked 
contrast with the crest. In summer, on a high bank like the Chesil, 
it is sheltered to the point of stifling. When investigated, doubtless 
the climatic factor (in the wide sense) will prove to be important 
on shingle banks and may well be correlated with plant-zonation. 
The Hooks —apart from the terminal hook—are notably passive 
and consolidated, and never fail to show a “ succession.” Among 
their distinctive plants may be mentioned Inula critlimoides (Hurst 
Castle, Hamstead Dover) and Liinoninm binervosum (Blakeney). 
The flanks of the hooks are under tidal influence and show a 
striking zonation in which the halophytes are conspicuous, whilst 
the flat summits bear a closed grassy “ gravel association.” As 
the shingle of the main bank advances over the hooks the vegetation 
of the latter reverts to the pioneer type. 
Shingle Banks of the apposition type show very distinctive 
features dependent on their isolation from the sea. This affects 
them in three distinct ways. They are essentially dormant; they 
lack the humous materials left by the tidal drift on other banks ; 
and they are denied the accession of seeds and other propagula in 
which the drift abounds. 
Consequently these vast areas of shingle (Dungeness, Rye) 
tend to remain long sterile. In the neighbourhood of habitations 
and.traffic many ruderal plants establish themselves, and sometimes 
1 No doubt when “ mobility” is more fully analysed and studied, 
a distinction based on the plants will be possible, e.g. between 
places of erosion and places of accumulation. 
