l6 THE CHICAGO ACADEMY OF SCIENCES. 



ing he has examined in the mineral collection. After a little 

 practice he is able to place them in their proper groups as 

 members of a class not mentioned in Dana's mineralogy the 

 class of cement side-walks, brick, furnace slag, coal from pass- 

 ing vessels, and broken bottles. He sees bright yellow flakes 

 on various rocks, and has to urge himself to classify these, not 

 among the precious metals, but as the scratches made by brass- 

 nailed shoes. But with these artificial products set aside he 

 soon learns to recognize the following minerals, which are 

 arranged for consideration in the classes and groups used by 

 Dana: 



