r 



E!r?:?fi!i; 



JUDGING THE AGE OF THE ROCKS 



We can see rivers cutting gullies through layer after layer of soil and rock. We as- 

 sume that rivers produced gorges and canyons in the same way through the ages. 

 We can see lakes, and even the seashore, filling up with silt. We assume that the 

 upper layers of mud and rock are more recent than the deeper layers 



