CARBONACEOUS ROCKS 33 
What could modern civilization do without them ? 
The geologist includes all these substances under the 
term “rock,” as is also the case with clay, marl, 
sand, and gravel. 
Peat is composed of partly decayed mossy plants ; 
it is fibrous in texture, compact, claylike, and quite 
black in the lower parts of a bed, but at the surface 
loose, and providing food for living plants which 
send their roots down into it. 
=~ aed = ae A on 
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Be gate RE ne OD 
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Fic. 3.—Sxzton oF Liu 
oF WHITE CHERT AT MippLETON Moor, DERBYSHIRE. 
Ingnite, also called “‘ Brown Coal,” is intermediate 
between peat and ordinary coal. It is decayed vege- 
tation that has been more chemically changed and 
subjected to higher pressure than that which forms 
peat. It may be regarded as fossil wood. 
Coal is mineralized vegetation—that is, decayed 
vegetable matter that has been mixed up with and 
buried in sediments, and under great pressure, and 
some chemical action, converted into the valuable 
mineral that it is. 
