CHAPTER XXIV. 



ELEMENTARY STUDIES OF SOME COMMON ROCKS. 



GRANITE. 



THEORETICALLY, perhaps, the expert teacher of nature 

 study should cull his lessons from the material most ready 

 to hand about the school. But in actual practice there is 

 no question that the most effective geological lessons will 

 be taught from carefully chosen material selected with a 

 view to its fitness for clear instruction wherever it comes 

 from. Local material may of course be discussed during 

 excursions or when pupils bring it in, but it does not 

 necessarily make suitable material for indoor lessons merely 

 because it is local. 



Now a lesson on Granite should be given off specimens 

 of as coarse-grained a granite as is procurable. Fairly 

 good types are the well-known granite of Shap (Westmor- 

 land) or Colcerrow (Cornwall) ; they may easily be got 

 from any dealer, or by writing to the quarries direct. Still 

 better is the " giant granite " (Pegmatite) found in veins 

 traversing granite quarries, and used in some localities 

 for building rockeries. Each child should, if possible, have 

 a specimen. The lesson may be conducted as follows : 



1. Emphasise the difference between a mineral and a 

 rock. It would be well for this purpose to procure a 

 tolerably big specimen of each of the three minerals, 



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