96 
F. W. Oliver. 
Hamstead Dover, whilst, so far as has been ascertained, there is 
only one locality for it on the Chesil Bank between Burton 
Bradstock and Wyke Regis (twelve miles). Now Arenaria peploides 
is one of the most characteristic of arenicolous plants and I have 
not the least doubt that its occurrence in all these cases is determined 
by sand which is present. The apparent anomalies of its distribution 
are therefore referable to fluctuations in the composition of the 
beach materials on the various banks. Other examples of the 
same kind could he cited, but this is not the place for a critical 
survey. 
The Okigin of the Soil in Shingle Banks. 
Isolated as they are in position and sterile in nature, shingle 
beaches and especially shingle spits entirely belie their appearance 
in regard to the soil which they contain. In point of fact the shingle 
spit is remarkable, if not unique, among plant habitats, for the 
richness of its outside supplies of humus-forming materials. And, 
in addition to these it retains, of course, the products of the 
disintegration of the vegetation which it bears. 
The great source of supply is derived from the drift, and this 
for convenience may be divided into that derived (1) from the open 
sea, (2) from the salt-marshes on the landward side. 
The drift from the sea is generally considerable in amount and 
includes the usual flotsam and jetsam—bits of wood, bark, corks, 
pine cones, seaweeds, and the like. These are lifted high up by the 
waves and are scattered by the wind as they dry over the crest and 
back of the bank. They may be found in all stages of disintegra¬ 
tion, and are readily “ assimilated ” by the open-textured shingle. 
Of much greater importance, however, is the drift from the salt- 
marshes left by the tides at the foot of the lee slope or on the 
terrace. The amount of this marsh-drift that becomes available is 
simply prodigious, and from the nature of the case, none of it is 
lost. The constant slipping of the shingle on this side of the spit 
ensures continuous inter-statification of humus and shingle like 
a sandwich of the “ Swiss roll ” variety. The process is always at 
work, and as a result the lower parts of the bank become thoroughly 
permeated. 
The new bank formed at Blakeney Point last Easter was 
examined from this point of view, and it was surprising to find what 
immense blankets of drift it had trapped. The horizontal lines of 
drift, visible in the photograph (PI. 4, fig. 2), give but an im¬ 
perfect idea of the richness within. The very storms which built 
