37 



CHAPTER III. 



DUST-MAKERS WIND, WAVES, RAIN. 



The Sand-blast, how it Cuts and Polishes How the Waves Work A 

 Shower of Rain, what causes it, what becomes of it Springs, 

 Land-slips, " Stone Rivers. '' 



OF late years a new way of grinding and etching glass 

 has been invented by an American. Instead of the 

 usual acid he employs fine quartz sand, which is driven 

 against the glass by a blast of air, and in from ten to fifteen 

 seconds removes all the polish from the surface. 



Window-glass exposed near the sea-shore soon loses its 

 polish in like manner from the natural sand-blast which so 

 often drives against it ; but the artificial sand-blast not 

 merely de-polishes but actually cuts through substances 

 harder than the sand itself. A solid block of corundum, for 

 instance, which is but little inferior to the diamond in point 

 of hardness, may be bored to the depth of an inch and a 

 half in five-and-twenty minutes ; while a quarter of an inch 

 of hard steel may be cut through in ten minutes, and in the 

 course of an hour a piece of marble half an inch thick can 

 be covered with an elaborate open-work pattern, such as it 

 would take many days to produce by the ordinary process. 



And now let us see what Nature has accomplished by 

 means of her sand-blast, which has been in operation for 

 ages past (Fig. n). 



In the neighbourhood of Suez the ground is thickly 



