ACTIOISr OF WIND 283 



in a state of almost constant, though it may be imperceptible, 

 motion, ever changing their shapes and moving onward like 

 long parallel drifts of snow. The rate of motion of a dune 

 from necessity is governed by the strength and constancy of 

 the winds, and the fineness and dryness of the sand. Urged 

 into temporary activity, each little grain goes scurrying up the 

 slope, across the crest, and tumbles to rest in the steeper 

 declivity upon the leeward side, to be slowly buried by those 

 which follow. This is the sum total of the movement taking 

 place in the march of a dune, whatever its pace and however 

 great its bulk. Yet in this very faculty of moving itself for- 

 ward by but a ten billionth part of its bulk at a time lies the 

 whole secret of its power. Silently, imperceptibly it may be 

 except when measured by months and perhaps years of time, 

 retarded by no walls nor ordinary declivities, it relentlessly 

 performs its task.^ 



A writer in one of the recent popular magazines estimates 

 the dunes of Hatteras and Henlopen as in some cases upwards 

 of 70 feet in height and moving at least 50 feet a year. Swamps 

 have thus been filled, forests and houses buried, and it is stated 

 that but a few years can elapse before the entire island lying 

 north of Cape Hatteras will be rendered uninhabitable. The 

 sand dunes on the coast of Prussia commenced but little more 

 than a century ago, and already fields and villages have been 

 buried and valuable forests laid waste by them. In one instance 

 a tall pine forest covering many hundred acres was destroyed 

 during the brief period intervening between 1804 and 1827. 

 Loftus, writing of Niliyga, an old Arab town a few miles east 

 of the ruins of Babylon, says that in 1848 the sand began to 

 accumulate about it, and in six years the desert within a radius 

 of six miles was covered with little undulating domes, while 

 the ruins of the city were so buried that it is now impossible 

 to trace their original form and extent. A still more striking 

 illustration of the rapidity of sand accumulations is offered 

 by the same authority in describing the burial customs of some 

 of these ancient people, it being stated that the earthen coffins 

 were merely stacked in layers one on top of another, and left 

 thus to be covered by the finer sand sifted over them by the 

 winds from the desert. Even Nineveh, founded some twenty 

 centuries before Christ and destroyed 1400 years later, became 



* The Wind as a Factor in Geology, Engineering Magazine, 1892, p. 596. 



