90 



THE NATURE BOOK 



iT •: .ju. - *• • 



POT HOLE AT THE BASE OF A WATERFALL CONTAINING ROUNDED 



STONES. 



been carried over the falls to swirl 

 round and round, and in turning they 

 have excavated the hollow by slow 

 degrees. 



The hollows are called " pot holes," 

 and at the bottom of each cavity we 

 see one or more smooth, rounded stones 

 which in abrading the rock have them- 

 selves become abraded. 



By contact with their fellows and with 

 the world about them, they have lost 

 their rough- 

 ness and an- 

 gularity and 

 have been 

 shaped into 

 smooth and 

 polished speci- 

 mens of their 

 kind. In the 

 u})per reaches 

 the stream, 

 full of youth- 

 ful vigour, and 

 impatient to 

 reach its goal, 

 cuts a channel 

 straight and 

 deep. It leaps 

 the obstacles 

 in its path, 

 rests a little 



in a quiet pool to 

 gather strength, and 

 then sets out again 

 on its impetuous 

 career. 



When it reaches 

 the plain b e 1 o w, 

 where the ground is 

 covered with softer 

 materials, such as 

 clay, mud, and sand, 

 it begins to meander 

 from side to side. 

 The slightest ob- 

 stacle, such as a fal- 

 len tree or a big 

 boulder, will cause 

 it to swerve from 

 the straight path. 

 At first the swings 

 are but little re- 

 moved from a 

 straight line, but as 

 v»'e proceed further 

 down-stream they become more and more 

 acute, until a big circular sweep is taken 

 which almost loops the stream on itself, 

 and onl}' a foot or so of soil prevents 

 the water from cutting across the barrier 

 and flowing on in a straight line.* 



When this has been accomplished it 

 once more pursues a direct and un- 



* Since the above was written (March, 1908) the 

 barrier has been cut through and the main current 

 has been diverted from the curved channel (see p. 93). 



"BY CONTACT WITH THEIR FELLOWS . . • THEY HAVE LOST THEIR 

 ROUGHNESS AND ANGULARITY." 



