MARBLE 



419 



of lime left by running water. Sedimentary rocks are very 

 abundant and form about four fifths of all the rocks of the 

 earth. 



There are various kinds of sedimentary rock just as there 

 are various kinds of igneous rock. Sandstone is one of the 

 most popular for building stone. It is abundant, easy to quarry, 

 and easy to dress. The red sandstone of Pennsylvania is par- 

 ticularly popular and is used extensively, especially in the eastern 

 part of the United States. The objection to sandstone for 

 building purposes is that it is soft and porous and easily weath- 

 ered. Buildings made of the very soft sandstone look old in a 

 few years. 



Marble. In the course of time, igneous rock and sedimentary 

 rock may lose their characteristics and become modified into 



FIG. 285. A quarry of metamorphic rock. 



new forms of rock. Lava which cooled underground may be- 

 come exposed to the atmosphere, and so lose its original char- 

 acteristics and become greatly modified in composition and 

 texture. Lava which cooled on the surface may become buried 



CLARK INTRO. TO SC. 2? 



