34 THE OPEN BOOK OF NATURE 
Anthracite (Greek, anthrax=carbon) bears the 
greatest amount of carbon of all the carbonaceous 
rocks. Itis vegetation even more highly mineralized 
than coal. 
A few words must now be said about the third 
great group of rocks called MrtTamMorputc. This 
term is derived from the two Greek words, meta = 
change, and morphe=form, and the metamorphic 
rocks are such as have been changed from their 
original condition by heat, pressure, and great earth 
Fic. 4.—DIAGRAM ILLUSTRATING BrpDs oF STRATIFIED Rooxs 
WHICH HAVE BEEN DISTORTED BY A FAvtt. 
movements. Molten rock, which has forced its way 
through fissures in sandstones to form dykes, changes 
the character of the sandstone which it touches ; its 
heat converts sandstone into quartzite. Certain 
sandstones have also been turned into schists. Both 
igneous and stratified rocks are subject to meta- 
morphism. Jfarble is altered limestone. What is 
known as Gneiss may be an altered granite. 
The earth movements which have raised up conti- 
nents and mountain-chains, and caused land surfaces 
