Building Materials, Their Use and Origin 415 



THE TYPICAL STAGES OF ROCK FORMATION 



SUMMARY 



Man needs protection from the weather and enemies, and a store- 

 house for food. 



Primitive protection was early replaced by buildings of stone and 

 brick among the Chaldeans and Egyptians. 



No building material meets all desired requirements. 



Wood, the most common building material, decays and is liable 

 to burn. 



Stone is preferred for fireproof structures. 



Sandrock is easily quarried and worked. It was formed by the 

 consolidation of grains of sand generally deposited in water. 



Slate is split easily along one plane. 



Granite is composed of particles of quartz, felspar, mica, and horn- 

 blende. It is difficult to work, but durable. It was formed by the 

 cooling and crystallizing of molten masses. 



Limestone is easily quarried because of planes of cleavage and 

 joints. It is easily worked and fairly durable. Caves found in lime- 

 rock are due to its solubility in water. Limestone is of organic origin. 



