ROCKS 5; 



ids upon unequal decay; some one or mo: 



< k disappear (aster than the others 

 h may remain isolated and comparatively little 



f the decomposed con- 

 stituent. 1 or exa: uany close-grained and crys- 

 talline rucks, consisting of quartz and felspar, these two 

 minerals are so intermingled and so resemble each other 

 in colour and lustre might not 



> . 



be distinguished ; but on a weathered surface their clearly 

 defined differences stand out very sharply ; the felspar 

 :res a dull earthy texture, while the irable 



quartz projects in hard glassy grains* A large number of 

 rocks are characterised each by its own type of weather- 

 ing. Thus, granite is apt to split along its joints and 

 to assume, as it decays, the aspect of ruined walls and 

 buttresses of cydopean mas< 50). Basalt-rocks 



