72
THE FIXATION OF SAND DUNES
are drifted inland by the wind; the inland dunes are largely bare, and hence inherently mobile; they also receive constant additions from the shore. Hence the general problem of fixation resolves itself into two distinct problems which are quite different in nature. In the first place, the sand from the shore must be
Fig. 14.—Chart of an Early Experimental Dune Planting by Soren BiSrn (1795)
The area shown covers roughly a quarter of a mile and slopes up from the shore. It is delimited by the brushwood fence aa. At bb is a planked paling which would perhaps form the crest of the new dune. At c is a high hurdling of Alder. The fences of the f series are low brushwood, whilst those of the k series are of living Poplar, with Salve ref>ens on either side (the dotted vertical lines). At dd are depressions occupied by brushwood tences placed crosswise. The larger areas at the top of the map were sown with Psamma seed (dotted), whilst the rectangular areas (some marked p) were planted with cuttings of the same (after Gerhardt).
prevented from adding itself to the inland dunes; it must be collected and fixed near the shore line in what is known as a littoral dune. The interior wandering dunes must be dealt with separately. Being no longer liable to accretion from the sea, it is simply a question of preventing their movement. The two parts of the whole phenomenon are therefore dealt with as