The Winds — Wind and Sand as Agents of Denudation — The Combat of the Inhabitants with Sand-laden Winds — The Dune-Belts — Origin of the Sand — Composition of Dune-Sand — The Forms of Dunes — Dimensions and Rate of Movement — Irresistibility of Blown Sand — Protection afforded by Topographical Features — Effect of Artificial Obstructions on the Formation of Dunes — Fixing of Dunes by Vegetation and Moisture — Storm-Walls and Fences — The Dunes of Gennâh — Wind-borne Sand beneficial in the South of the Oasis — Formation of Terraces of Wind-borne Materials — Encroachment of Dunes in the South of the Oasis. No one who has sojourned in Kharga long enough to compare it with other parts of Egypt will feel inclined to dispute the statement that the depression is one of the most windy places in the country. Only one day in ten or eleven is calm, though if the wind has been blowing fairly steadily during the day it generally drops at night. Five times out of six its direction is from the north, and when unaccompanied by sand the wind acts as a welcome moderator of the temperature. In a desert region, owing to the surface being unprotected by vegetation, there is nearly always an abundance of weathered material loosely exposed on the surface, the lighter portions of which are quickly swept up and carried along as soon as the wind attains even a moderate velocity. On the actual dunes even a light breeze is sufficient to set the surface-layers in motion, while on the open plain the wind becomes visibly charged with sand directly it attains the velocity of a moderate breeze. The frequency with which the wind blows has already been mentioned, and when we add that on one day in three it attains a velocity sufficient to enable it to easily carry sand in suspension, its power as a transporting agent can readily be conceived. Not only does the wind carry the sand along from one place to another, dumping it behind or in front of every obstacle it may meet, but the combination of sand and wind forms a denuding force of no mean power, capable of planing and grooving the exposed surfaces of the hardest of rocks.