APRIL 197 



we judge that the cooling must have taken place under 

 great pressure. 



The essential constituents of granite are feldspar and 

 quartz. Usually either mica or hornblende is present, 

 more commonly the former. 



Feldspar is always the most prominent constituent, 

 and gives to the granite its distinctive color, — white, 

 gray, red, pink. 



Method : 



This stone is so much used for building that pieces of 

 it are easily procured in sufficient quantities. 



Is this rock made up of one or several minerals ? How 

 many ? What colors ? Investigate the black mineral. 

 Is it hard or soft ? What is its structure ? its lustre ? 

 its name? Investigate the pink. What is its name? 

 How do you know ? Investigate the third mineral. 

 What is its name ? How do you know ? 



Of what, then, is granite composed ? Where is it 

 found ? What is it used for ? Wliy ? Does it ever 

 make soil ? How ? Describe the appearances of this 

 soil. 



Gneiss. 

 Facts : 



This is the commonest and therefore the most important 

 of all the rocks. It is undeniably of very ancient origin ; 

 but whether of aqueous or igneous structure is not yet 

 settled. It is often found with the habit of granite, and 

 even passing into it by gradual transitions. It is also 

 often found with the habit of an aqueous rock, of which, 

 indeed, it may be only a metamorphosis. 



Like granite, it is composed of feldspar, quartz, and 



