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F. W. Oliver. 
proper height, if it he excessive the result is to drive the shingle 
over the marshes and at the same time to reduce the height of the 
crest. 
B.—PERCOLATION. 
With the above is to be contrasted the landward displacement 
of shingle as a consequence of percolation. As a result of its open 
texture, shingle is readily traversed by water. On the Blakeney 
Bank towards the time of high tide, when the sea level outside is 
well above that on the marshes, and especially when a heavy sea 
is running, sea-water normally traverses the bank, breaking out 
on the lee side just above the level of the saltings in numberless 
springs. This phenomenon is accompanied by the displacement of 
a certain amount of shingle, but, regarded as a factor in the general 
landward creep of the bank as a whole, this displacement is relatively 
unimportant, owing to the small height of the bank above high water. 
In cases, however, like the Chesil, where the bank rises to a 
height of 20 feet or more above tidal limits, and usually at a steep 
angle which often approaches the critical angle of rest of the 
component materials, the results of percolation are both striking 
and important. 
If the Chesil Bank be viewed from the mainland at, e.g., a 
point east of Abbotsbury, its landward or N.E. face appeal s as a 
cliff scored by a series of deep ravines. Our photograph (PI. 4, 
fig. 1) provides such a view taken from the foot of Chesters Hill, 
two miles east of Abbotsbury. Over the Fleet, here about 400 yards 
in breadth, the bank rises from a low terrace which is fringed along 
the water’s edge by a line of bushes of Suceda fmticosa (conspicuous 
in the photograph). This terrace, foreshortened in the picture, is 
just above the water-level and has an average width of about 70 feet. 
The slope of the bank from the terrace is steep for the first ten or 
twelve feet; the gradient then becoming more gentle as the summit 
ridge or crest is approached. 
At the back of the terrace the foot of the slope is carved into a 
series of deep ravines which reach a height of 10—12 feet, and 
with the intervening buttresses form the conspicuous relief of the 
photograph. The back and sides of the ravines are formed of bare 
shingle inclined at the angle of repose (about 34°); bare shingle 
likewise forms the floor which is generally scored by a low gully 
connecting with a detrital fan of shingle projecting out into the 
Fleet some eight or ten feet beyond the edge of the terrace. 
