62 DIVERSIONS OF A NATURALIST 



currents caused by wind and tide, is the cause of this 

 variation and local difference. The pebbles of the 

 " beach " are, of course, always being worn away, rounded 

 and rubbed down by their daily movement upon one 

 another, caused by the waves as the tide mounts and 

 again descends over the shore. Even the biggest stones, 

 excepting those which lie in deeper water beyond the 

 beach, are eventually rubbed down, and become quite 

 small ; but a point is reached when, the weight of the 

 pebbles being very small, they have but little effect in 

 rubbing down each other, and consequently where the 

 pebbles consist of very hard material — like flints — the 

 smallest ones are not so much rounded, but are angular 

 and irregular in shape. 



Whilst a perfect gradation in size can be found from 

 the largest flint pebbles some 6 inches or 7 inches long 

 to the smallest, usually not bigger than a split pea 

 (though sometimes a patch of even smaller constituents 

 may be found), there is a real break or gap between 

 " pebbles " and " sand." I am referring now to what 

 is commonly known as " sand " on the southern part of 

 the East Coast, much of the South Coast, and the shores 

 of Holland, Belgium, and France. There are " sands " 

 of softer material (limestone and coral sand), but the 

 sands in question are almost entirely siliceous, made up 

 of tiny fragments of flint, of quartz, agate, and hard, 

 igneous rock. They are often called " sharp " sand. 

 The particles forming this sand are sorted out by the 

 action of moving water, and form large tracts between 

 tide-marks looking like brown sugar, for which baby 

 visitors have been known to mistake them, and accord- 

 ingly to swallow small handfuls. The strong wind from 

 the sea blows the sand thus exposed, as it dries, inland 

 out of reach of the tide, to form sand-dunes, and it is 



