SEDIMENTARY AND METAMORPHIC ROCKS 
105 
CLASSIFICATION OF THE COMMON METAMORPHIC ROCKS 
NATURE OF 
METAMORPHISM. 
KIND OF ROCK. 
SOURCE. 
Less extensively met- 
amorphosed rocks. 
Origin not difficult 
to detect. 
Conglomeratie quartzite. 
Conglomeratic schists. 
Metamorphosed from 
conglomerate. 
Quartzite. 
From sandstone. 
Slate and certain schists. 
From clay rocks. 
Marble. 
From limestone. 
Certain anthracite coals 
and graphite. 
From vegetable de- 
posits. 
Certain schists and 
gneisses. 
From igneous rocks. 
So metamorphosed 
that the origin can- 
not be ascertained. 
Most schists and gneisses. 
Some iron beds and mar- 
bles. 
In some cases, pos- 
sibly, originally 
formed this way. 
In others, evidently 
changed beyond 
recognition, pos- 
sibly from igneous, 
possibly from sedi- 
mentary rocks. 
