64 THE SAND STRAND FLORA 



It is the natural border between the Bay of Biscay and the territory 

 known as the "Landes.'' The sand had for centuries been constantly 

 shifting, making great devastations, until its progress was arrested by 

 plantations. Engineering skill and judicious planting of sandstays and 

 trees has changed this district from desolate, unhealthy marshy moor- 

 lands and unproductive sandy tracts to a habitable, and in some places, 

 fertile country. 



According to early writers, the dunes advanced in fornier times con- 

 stantly inland covering houses, filling the outlets of rivers, making great 

 damages to cultivations and increasing the unhealthiness of the Landes. 

 The advance of the sand was especially rapid in the neighborhood of 

 Saint Pol-de-Leon; there existed before the year 1666 several villages 

 which had to be abandoned, and which were buried under 6 and 7 m. 

 of sand. In 1722, this dune had progressed more than 24 km., which 

 would indicate a yearly advance of more than 500 m. According to 

 Bremontier, the dimes advanced at his time, or about 1790, from 20 to 

 25 m. a year, and they did great damage to the fields in the neighborhood 

 of Bordeaux. 



The whole coast from Gironde to the foot of the Pyrenees presents 

 an aspect in regard to its geological constitution, quite uniform with 

 the sandy coast in the north. Capbreton, situated at the ancient estuary 

 at I'Adour, at the present day covered with dunes, was formerly a 

 flourishing harbor, which has since been replaced by Bayonne. The 

 dunes on this coast are often high, in some places averaging 70 m. 



The sand is composed of pure quartz, reduced to minute grains, 

 generally rounded by trituration, and moving easily. The width of the 

 upper beach is aJDOut 200 m. from highwater mark to the foot of the 

 littoral dune. 



The dunes form a series of parallel ridges, the valleys being of vary- 

 ing width. Whenever the dune valleys, locally called "Lettes"', reach a 

 width of 1 km. they are covered with a luxuriant vegetation. 



The most frequent winds, and the most violent ones on this coast, 

 are those from the west and south west. 



AUSTRALIA. 



Sand formations on the west coast 



are very common on this island-continent. At Geraldtou they are quite 

 high and are constantly shifting. North and South of Fremantle there 

 is a dune district of considerable extent, and this was studied in the 



