“PART IV. 
NAMING ROCKS. 
EXPLANATION OF TERMS 
Rocks are mineral aggregates, or in other words. 
they are inorganic substances formed by the chemical or 
mechanical union of two or more minerals. Rocks, like 
minerals, exhibit different forms and various physical 
and chemical characteristics, certain terms are applied 
to rocks in accordance with these features, by which 
their appearance and structure are broadly expressed. 
For example: A rock, when sandy, is said to be arena- 
ceous ; or when it is clayey it is called argillaceous ; when 
it contains much lime it is called calcareous; or much 
silica, it is termed silicious. 
A sedimentary rock is one which has resulted from 
the chemical or mechanical precipitation of sediment. 
An aqueous rock has been formed by the action of 
water: 
An igneous rock is one which has its origin in fire, 
either directly or indirectly. 
A stratified rock is one in which the lines of de- 
: posit are clearly marked in layers and such layers point 
to aqueous origin. 
An unstratified rock, on the contrary, has no such 
lines, and with one or two exceptions such rocks are of 
igneous origin. 
Metamorphic rocks are those in which some change 
has been induced due to crystallization after deposit. 
The term metamorphic is generally restricted to rock 
formerly of sedimentary or aqueous origin. 
