394 Salisbury. — The Soils of Blakeney Point : A Study of Soil 
Thus Psamma arenaria plays two important roles. On the one hand 
it helps to stabilize the sand mass against wind action, and on the other 
adds colloidal material by which the water-content is increased and the 
necessary medium provided for bacterial activity. 
In the outermost dunes on the sea face (cf. G, Text-fig. i) Psamma 
arenaria is the only important species, but on the new spit (j, near. 19 
and 20) of shingle Triticum junceum also forms embryo dunes. 
These early stages are represented by the series of samples G 01-G 029 
and J 030-J 036. The very small new dunes actually form several groups 
on the sea face, and such also occur on the new spit (samples J 032-J 036) 
and close to the Lifeboat House on the shore of the estuary (samples 
J 030-J 031 and J 022-J 024). For convenience these, together with the 
rather older stages represented by the series of samples F 01-F 021, may 
be termed collectively the young dunes. 
The next phase in the succession is represented by the samples E 1- 
E 31 from the main dune ridge (E, Text-fig. 1), where there is complete 
coalescence between the original units to form the highest ridge of the series. 
Psamma arenaria , though still the dominant species, is accompanied by 
Festuca arenaria and ephemerals such as Myosotis collina , Phleum arena - 
rium , Stellaria bore ana, Cerastium semidecandrum , &c. ; Senecio jacobaea is 
also of common occurrence. 
This phase as a whole may be conveniently termed the ‘ main ridge ’ 
and represents an advance in stability and organic content. It furnishes 
the culmination of the ‘ yellow dune ’ phase with which the marram grass 
is particularly associated. 
Still passing landwards we come to two more ridges (d and c, Text-fig. 1) 
parallel to the preceding system but comparatively low in height, due to 
the combined effects of ‘settling’, loss by erosion, and greatly diminished 
accretion. The profile no longer presents a narrow ridge, but a broad, more 
or less flat top, and, associated with the changed conditions, Psamma is 
much less vigorous, whilst mosses and lichens, especially Cladonia , mark the 
advent of the ‘ grey dune ’ phase and from their abundance constitute an 
effective protection against wind action. Here too are encountered the 
highly efficient sand binders Carex arenaria and Convolvulus soldanella , 
which, however, attain their greatest vigour where the sand has again been 
rendered mobile by undercutting. This type is represented by the series 
of samples D i-D 45 from the Laboratory ridge, and the series C 20-C 47 from 
the older and more stabilized ridge on its landward side. Two still older 
phases are represented respectively by the Long Hills (b, Text-fig. 1, samples 
B i-B 22), where alone on the area Polypodium vulgare occurs, and the Hood 
(a, Text-fig. 1, samples A i-A 16). 
Although the Hood is almost certainly the oldest dune mass on the 
area its comparatively small size and its isolated and exposed position 
