yee Ta a ee a, % 
-boniferous shale, flints from the chalk cliffs, or boulders from 
shore, and is found, with very few exceptions, accumulated — 
110 Burton: Lincolnshire Coast Boulders. 
‘ Material of littoral drift. The material may be classed 
as rock fragments, boulders, shingle, sand, and_ alluvial 
‘Sand. The material next in size, or that generally known 
as sand, becomes distributed by the waves on the shore, where 
r 
it is rolled backwards and forwards by the action of the tides ; 
but, under the action of gravity, having a continuous downward 
movement until the shore assumes a slope of from 1 in 30 to 
1 in 100, at which it attains a state of equilibrium.’ 
‘Where there are no cliffs to supply fresh material, sand- 
beaches are not subject to littoral drift, and, except to the 
extent already mentioned, little or no change takes place in 
their condition. They generally extend out from the line of 
high water of spring-tides to that of low water at a very flat 
slope, beyond which the slope becomes steeper.’ 
Thus, for example, on the east coast of England the drift 
from the material derived from the waste of the Yorkshire cliffs 
stops on the north side of the Humber. From the south side of 
that river to the Wash there extends for 25 miles a low tract of — 
flat country, bordered by hills of blown sand. The yi 
consists of sand which extends out at a slope of about 1 in 3 
to low water. On this beach there is no appreciable fiecaesl 
drift or alteration in form. Sand does not accumulate against 
the piers or groynes which extend across the shore; and the 
general outline of the beach remains as it always has been so . 
far as any record exists.’ * 
‘ Shingle. The supply and movement of this material is of 
much greater interest than either that of sand or alluvial matter, 
inasmuch as where it is forthcoming shingle forms one of the — 
most important aids to coast protection. 
‘The supply of shingle is obtained from the destruction of - 
cliffs consisting of granite and similar rocks or the hard, car- _ 
the Glacial Drift.’ . 
‘Shingle, unlike sand, becomes heaped up in banks on “the 
in a zone lying between low water of neap-tides and high water 
and the Chesil Bank, that the bank has been forced beyond | the 
jae limits.’ 
The banking up of the shingle and also the travel along the 
shore i is due entirely to tidal action. 
