174 FIRST YEAR COURSE IN GENERAL SCIENCE 



column, which increases in size as the trickling water 

 deposits more and more material. The Mammoth Cave 

 in Kentucky, the Luray Caverns in Virginia, and the 

 caves of the cliff dwellings in Colorado are the result of 

 the dissolving and removing of limestone rock by under- 

 ground waters. 



197. Marble. Calcite which has been changed from the 

 ordinary form of limestone to a crystalline condition is called 

 marble. A broken piece of marble has a glistening look, 

 because every face of the tiny crystals of which it is com- 

 posed is smooth and shining. The Washington Monument 

 and many public buildings at the national capital are built 

 of coarse-grained marble. Statuary is made of a finer 

 grained marble, free from stains. The marble quarried at 

 Carrara, Italy, is highly prized for this purpose. Most of 

 the marble used for building in the United States is from 

 Vermont; quarries in Tennessee furnish much of our marble 

 for interior use. 



198. Gypsum. Gypsum is a sulphate of lime. It is a 

 white mineral which is found dissolved in sea water and is de- 

 posited after the water evaporates. It is sometimes found in 

 large masses of rock. When fine and translucent, it is called 

 alabaster, and is used for ornaments. A coarser kind of gyp- 

 sum, on being heated, crumbles to a powder, which is called 

 plaster of Paris. This is used extensively as a wall finish. 

 If water is added to the plaster, it soon hardens into a solid 

 mass. In this way, it is used by artists to make plaster casts, 

 and by surgeons to form a rigid support for a broken limb. 



199. Petrifactions. When plants and animals decay 

 under the ground and in the presence of water containing 

 dissolved mineral matter (such as silica or calcite), the min- 

 eral sometimes takes the place of the decaying material. 

 Although the old form and frequently the old color remain, 

 a stone body results. This is called a petrifaction or a 

 petrified body. 



