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CLASSIFICATION OF THE ROCKS. 153 
Classification of the Rocks—Description of the Rock-Systems, 
We now proceed to describe, in the order of their formation, the different 
kinds of rocks that compose the crust of the earth, and their fossil con- 
tents. As already said, geologists have divided all the rocks into different 
classes, according to their relative position and the fossils they contain. 
The whole of the rocks are divided into twelve great systems, and each 
of these into separate groups, to which names have been given, more 
or less descriptive of the strata to which they are applied. These 
systems we shall describe in order, beginning with the earliest, down to 
the most recent, giving the appearance and composition of the rocks, 
the uses to which they are applied, and the fossils they contain. We 
shall also endeavour to realise the state of the earth at each successive 
epoch, the scenery then exhibited, and the plants and animals that then 
enlivened the landscape. Before doing so, it is interesting to ask— 
What Rock is oldest and lowest ?—What rock is the foundation on which 
all others rest? On the answer to this question, geologists are not agreed. 
We know the oldest sedimentary rock; and though the above question 
were to remain unanswered, the science of geology proper would be as 
complete as it requires to be. But some approach can be made to an 
answer. Granite seems to underlie all other rocks ; at least, as far as yet 
ascertained, no other rock has been found under the granite, and this 
rock is erupted through all other strata ; but we cannot assert definitely 
that this is the primitive or oldest rock, but only that, as far as yet dis- 
covered, no other has been found to underlie it. All are familiar with this 
beautiful variegated rock as used for paving our streets, and as polished 
for gravestones and hewn into pillars. It has two chief varieties, the gray 
and the red, according to the prevailing mineral in its composition. It 
composes the mass of the chief mountain ranges, and forms part of some 
of the grandest scenes in nature. It is generally considered to be of 
igneous origin. It shews no stratification, occurs only in great mountain 
masses, or in veins intersecting other strata, and seems to point to a period 
in the past history of our globe when it was a great molten ball, with 
conditions that we can scarcely imagine, so different must they have been 
from those now existing. But it seems to be undeniable, that before any 
_ of the stratified rocks were deposited, and before any life existed, the globe 
was in a state of molten fusion through intense heat ; and that we have 
before us, in the granite, the remains of that igneous condition, which now 
exists as a cold, crystallised, variegated rock, containing valuable minerals, 
and of great industrial value, 
