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F. W. Oliver . 
bank “ as a result of the eastward deflection by the bank of the 
streams which descend to the shore eastward of Abbotsbury ” (cf. 
Text-fig. 5). This theory finds an able exponent in Mr. Aubrey 
Strahan, whose evidence before the Royal Commission on Coast 
Erosion should be consulted on the matter. 1 
Though it is superfluous to recapitulate the facts on which this 
view is founded, there is one feature pointing in the same direction 
which has not perhaps been adequately emphasized. The curvature 
of the Chesil presents its concavity to the sea, and in this seems 
inconsistent with a spit type of development. 
If we assume the truth of this theory, which is certainly 
attractive, the Fleet or lagoon behind the Chesil Bank, though not 
ontogenetically the equivalent of the salt-marshes which usually 
lie on the protected side of a shingle spit, may nevertheless be 
regarded as playing the same functional role —a point which will be 
elaborated in further detail. 
On the Mobility of Shingle Banks. 
It is not proposed here to consider the mobility of shingle in 
general or the phenomena and laws of its drift below tide-marks. 
To a botanist legitimate interest only begins when the shingle has 
been thrown up high and dry to form a habitat capable of invasion 
by plants. The height to which shingle is raised doubtless depends 
upon a combination of factors of which the chief are the height and 
velocity of storm-waves and the presence or absence of deep water 
at the foot of the bank. The crest of the Chesil Bank has a S.W. 
exposure and rises out of deep water twenty to twenty-five feet above 
the high-water mark of ordinary spring tides; that of the Blakeney 
Bank with a northerly exposure and shoaling shore, six or seven 
feet; whilst the Hamstead Dover, in the protected waters of the 
Solent, rises no more than a bare two feet. But when the shingle 
has reached the crest it finds no permanent place of rest, except in 
banks of the apposition type, where a newer ridge will be thrown up, 
isolating the last from the influence of the surf. 
So long as the sea beats on a shingle bank, so long will its 
component parts be liable to motion, unless it be covered and pro¬ 
tected by dunes or—what very rarely happens in Nature—becomes 
so densely clothed and bound with a robust vegetation as to defy 
the violence of the elements. 2 
1 Minutes of Evidence, Royal Com. on Coast Erosion, Vol. 1, pt. 
2, 1907, esp. answers Nos. 3624-3718, pp. 133-136. 
2 The Calshot Spit bears dense mixed scrub and a few trees. 
