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SAND-DUNES AND BLOWING SAND. 
By W. TOPLEY, F.G.S., 
Assoc. Inst. C.E., Geological Survey oe England. 
T HE action of the wind and waves upon our coast affords a 
most interesting field for study. On first looking into 
the subject, we cannot but be struck with the widely different 
effects which are produced by similar causes. We see the coast 
of Holderness yielding to the waves at the rate of from two to 
three yards per year ; a few miles further south, at Spurn 
Point, we find that the same causes produce an oscillation of 
land and sea, sometimes the former and sometimes the latter 
gaining the mastery, but the nett result of which has been to 
prolong the point to the south ; in other places (as at Dunge- 
ness) the gain of land is constant and rapid. We say the same 
causes produce the results, but it is manifest that the surround- 
ing circumstances must vary greatly in the different cases 
Shingle sometimes acts as a destructive agent, being hurled by 
the waves against the land ; elsewhere it forms a long line of 
defence, keeping the relative areas of sea and land unchanged ; 
in other places the shingle accumulates, and increases the area 
of land. 
The material with which we are now alone concerned is, at 
first sight, of little moment. Sand is proverbially weak and 
unstable, and one might well doubt if, either as a destructive 
or preserving agent, it could have much effect upon the advance 
of the sea; but plain facts show us that its effects are most 
important. 
The space between high and low water mark varies very 
greatly in different parts of the coast, both as to its width and 
the materials of which it is composed. Sometimes it is formed 
of rock, sometimes of mud, shingle, or sand. When shingle is 
accumulating, as also in some beaches which are stationary, the 
whole slope is generally formed of pebble ; but the more common 
arrangement is for the shingle to occupy only the upper part 
of the foreshore, generally to about mean sea level ; below that 
