THE GEOLOGIST. 
63 
I have here to request that, for the present at least, it may be 
taken for granted that the beds or strata are presented in regular series 
or succession, containing the remains of ancient animals and plants, 
whicli have been of very different characters, at those different periods, 
or systems, into which the past history of our own planet is divided. 
Probably many of my readers will have acquired much of this 
elementary information from the numerous popular treatises which 
have been produced by so many of our eminent geologists, although 
there are still many to whom even these primary tenets of our science 
will be new. For their sakes, therefore, I repeat that which I know 
to be familiar to others. 
Even those who know the general features of the science will not 
suffer by a repetition occasionally of the knowledge they have acquired, 
and as never an artist who sits down to draw an oft-repeated scene pro- 
duces a fac-simile of his predecessors' works, so the geologist, though he 
repeats an old tale, still embodies something of his feelings and of 
himself in the new picture which he paints. The accompanying tables 
will display the principal divisional arrangements of the various earths 
or rocks, and will aid tho uninitiated reader in following our remarks. 
rNSTRATIFIED EOCKS. 
Plutonic. 
Rocks subjected to heat be- 
neath the surface and not 
ejected like lava, although 
often protruded in rugged 
masses through the disrupt- 
ed beds of stratified rocks. 
Example : 
Granite. 
Volcanic. 
Rocks the produce of 
ancient volcanos ; often 
ejected as in modern 
eruptions. 
Examples — Basalt, Trap, 
Lava. 
STEATIFIED ROCKS. 
Rocks formed by the deposition from water of the sediments derived 
from pre-existing materials. These are grouped into great divisions 
called systems, representing periods in time, the rocks thus associated 
together having a collactive relationship. The members of each group, 
while presenting also some general linking features among themselves, 
are nevertheless marked by distinctive characters which more or less 
separate them from each other. 
