328 H. C. Wilmer.— The Relation of the Sand Dune [July 31, 



of the desert surface as already described ; and as it meets the 

 resistance of the colder and denser stratum of air from the sea, also 

 struggling towards the vacuum, its force gradually becomes exhausted, 

 and, as it dies away, it deposits its suspended partisles of sand and 

 mica, partly on the coast and partly in the sea. Some of that which 

 falls into the sea is carried along by the current, which runs strongly 

 to the North, until a submerged reef of rocks is met with as at 

 Sandwich Harbour and Angra Pequena, when a portion of the sand 

 is arrested, the bank thus formed eventually rising above the surface ; 

 and thus are formed the sand spits, always trending northwards, by 

 which the bays of Sandwich Harbour and Walfish Bay are protected 

 from Southerly and Westerly winds. 



Having thus shewn the effects of the sand dunes and desert on the 

 local winds, we will now consider the relation of these currents to 

 the progressive motion of the sand dunes from North to South. Dr. 

 F. M. Stapff, of Weissensee near Berlin, has, in his report to the 

 German Colonial Society in 1886, concluded that the sand dunes of 

 the South-west coast were formed under the sea and afterwards 

 raised above its level. This is an entirely erroneous conclusion, 

 resulting from cursory and superficial observation, as I will proceed 

 to shew. In the first place the enorinous quantities of sand, brought 

 to the coast by the East wind and partially deposited near the shore 

 as already explained, are quite sufficient to account for the extent 

 of the deposit. Secondly, there is a total absence of shells or other 

 organic remains of marine life in the sand of the dunes. Again the 

 sand hills are ever advancing to the North. This is caused by the 

 alternate action of the East wind and the South-west, which is diagonal 

 to the direction of the former, and thus the sand being first pushed 

 to the West and then back to the North-east, gradually extends itself 

 to the North. 



In this way the sand hills have, in the course of ages, been advanced 

 to the North extending the desert as they extended, until they reached 

 the Kinsib river. They have completely choked and obliterated the 

 lower courses of several minor rivers, such as the Choondap and others, 

 which now disappear under the eastern edge of the sand dunes. The 

 Kinsib river still sends down sufficient water in years of plentiful rain 

 in the interior to clear its bed of the sand dunes formed in it in the 

 intervals and thus keeps a road from Walfish Bay, where it debouches, 

 open to the interior. The river ran to the sea in 1856, 1864, 1881, 

 and 1885, and the long intervals between gave the sand hills time to 



