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THE FIXATION OF SAND DUNES
holding wandering dunes no longer receiving fresh supplies of sand the Tree Lupin (Lupinus arborea) is recommended. This plant has no capacity for ascending to the surface in drifting sand, but it readily establishes and covers the ground till such time as the dune can be permanently afforested. Being a member of the family Leguminosae, this plant, through its nitrogen-fixing root tubercles, exerts a favourable influence on the soil. For afforestation purposes Dr. Cockayne speaks in the highest terms of Pinus insignis, which we have reason to believe would prove successful in Britain. The tree is famous for its rapid rate of growth. He also draws attention to Cupressus macrocarpa.
   Successful plantings of Psamma have also been established in Australia at Port Fairy (Victoria) and elsewhere.1 The photographs of Plate VII show the first planting in progress, and the results after three years’ growth. In the lower picture, cuttings of Psamma are being dug to continue the planting elsewhere. Plate VIII, 2, shows a recent dune planting on the Southport dunes (Lancashire) taken in 1911.
   Holland is a country the existence of which depends on the maintenance of its sand dunes. These vary from 1 to 3 miles in width, and rise to a height of 130 feet. Essentially Holland has been fashioned by the skill and industry of its inhabitants out of the alluvial matter brought down by the Rhine and Maas, and accumulated behind a seaward belt of sand dunes, somewhat on the pattern of the Kurische Nehrungon the Baltic. The initial stages of Holland were laid down, according to the prevailing theory, at a time when the Straits of Dover had not yet opened, and the North Sea was, like the Baltic, a tideless gulf into which the Maas, Rhine, Ems, Weser, and Elbe discharged. When the English Channel became continuous with this gulf, and the tides gained access, the hitherto continuous chain of dunes was largely broken into the fragments now known as the Frisian Islands. A further expression of these more strenuous conditions was the inrush of the waters to form the Zuider Zee and the Dollart. The longest surviving strip
    1 See J. H. Maiden, “The Sand-drift Problem in New South Wales", in Tfu Forest Flora of N.S. W., pt. lvii, X915.