SAND-DUNES 



931 



. vkEEP OF A SANDY BAY. 



and the waves are the power which Nature 

 has used in the process of grinding down 

 these countless sand grains. The granites, 

 gneisses, and crystalhne schists, wherever 

 they form the coast-hne, have contributed 

 largely to the formation of the sands, 

 though the denudation of the sea-cliffs 

 under the action of the atmosphere, land- 

 springs, and the waves cannot adequately 

 account for the vast masses of sand to 

 be found along our coasts. Probably a 

 very large amount of the material, which 

 in the course of geological ages Nature 

 has converted into the golden sands that 

 now fringe the sea coast, was originally 

 transported shorewards from the hills 

 and mountains by the glaciers and torrents 

 of the Ice Age ; and during the succeeding 

 ages the debris so transported has been 

 broken down, sifted, and distributed as 

 sand and shingle by the waves. 



It is very interesting to observe the 

 characteristic difference of form which 

 exists between the sands of the sea- 

 shore and the sands of the great inland 

 deserts. The sand grains on the sea- 

 shore wiU always be found to retain to a 

 certain degree their angles ; and this 



characteristic peculiarity is due to the 

 wet grains lying with their faces to one 

 another holding a film of water between 

 them, which keeps the grains from actually 

 touching each other, and consequently 

 greatly reduces the friction between the 

 sides of the grains, which would otherwise 

 wear down the angles. On the other 

 hand, the sands of the desert are absolutely 

 dry and destitute of this protecting film 

 of water, consequently they are blown 

 about by the wind, and beating against, 

 and roUing over, each other, become 

 rounded, and finally converted into dust. 



On the confines of the Isle of Purbeck, 

 from the entrance to Poole Harbour to 

 Studland Bay, stretches a wide expanse 

 of beautiful sands, where one may spend 

 a long summer afternoon collecting the 

 many rainbow-tinted shells that have 

 been left exposed by the gently lapping 

 waves of the receding tide, or wander 

 along the sands at, and above, high- 

 water mark where the sand-dunes are 

 forming, and where every stage in the 

 process of their formation may be seen. 



The factors that play the most im- 

 portant part in the formatifjn of the sand- 



