24S 



THE NATURE BOOK 



is really effective 

 in abrasion and 

 polishing. 



We have seen 

 that moving water 

 in the form of a 

 ri\'er can cnt gorges 

 and excavate wide 

 valleys. The sea, 

 when lashed into 

 great waves, not 

 only hurls huge 

 masses of water 

 against the cliffs, 

 but bombards the 

 rocks with showers 

 of stones ; it is 

 these missiles 

 which drill caves 

 and isolate stacks. 



When we come 

 to discuss v^alleys 

 we shall see how 

 important are the 

 effects of moving 

 ice in moulding the 

 contours of the 

 land. In some parts 

 of our own islands 

 ancient glaciers are still to be seen. 



THE DRIVEN PARTICLES ETCH OUT THE 



SOFTER PORTIONS." 



Sand-etched rocks at Burton, Cheshire. 



the tool marks of 



severed and expose 

 ing forces. 



We can study 

 the effects of mov- 

 ing air in a dusty 

 road or on a sandy 

 beach. The wind 

 catches up grains 

 and flings them 

 against any object 

 in its path. In this 

 way windows of 

 dwellings and light- 

 h o uses facing a 

 sandy beach become 

 frosted by the 

 natural sandblast. 

 If the obstacle is not 

 composed of ma- 

 terial of equal 

 hardness, the driven 

 particles etch out 

 the softer portions 

 and leave the 

 harder standing out 

 from the face. 



By long con- 

 tinued action great 

 rock masses once 

 continuous become 

 the interior to denud- 



J. LOMAS. 



"MASSES ONCK CONTINUOUS BECOME SEVERED.' 

 Brimhain Rocks, Millstone Grit. 



liXrafh I'y O. Bin^iey, ileadingley. 



