
2 GEOLOGY. 
the botanist, the zoologist, even to the unscientific, if observant, 
traveller by land or sea, the geologist turns for information and 
assistance. ee 
But while thus culling freely from the dominions of other 
sciences, geology claims as its peculiar territory the rocky frame- 
work of the globe. In the materials composing that framework, ~ 
their composition and arrangement, the processes of their formation, — 
the changes which they have individually undergone, and the grand — 
terrestrial revolutions to which they bear witness, lie the main data — 
of geological history. It is the task of the geologist to group these ~ 
elements in such a way that they may be made to yield up their 
evidence as to the march of events in the evolution of the planet. 
He finds that they have in large measure arranged themselves in 
chronological sequence,—the oldest lying at the bottom and the 
newest at the top. Relics of an ancient sea-floor are overlaid with 
traces of a vanished land-surface; these are in turn covered by the 
deposits of a former lake, above which once more appear proofs of 
the return of the sea. Among these rocky records lie the lavas and 
ashes of long-extinct volcanoes. The ripple left upon the shore, the — 
eracks formed by the sun’s heat upon the muddy bottom of a dried-— 
up pool, the very imprint of the drops of a passing rain-shower, have 
all been accurately preserved, and often bear witness to geographical 
conditions widely different from those that exist where such mark- 
ings are now found. 
But it is mainly by the remains of plants and animals imbedded - 
in the rocks that the geologist is guided in unravelling the chrono- 
logical succession of geological changes. He has found that a 
certain order of appearance characterises these organic remains; that 
each great group of rocks is marked by its own special types of life; 
that these types can be recognised, and that the rocks in which 
they occur can be correlated, even in distant countries, where no 
other means of comparison is available. At one moment he has to 
deal with the bones of some large mammal scattered through a deposit. 
of superficial gravel, at another time with the minute foraminifers— 
and ostracods of an upraised sea-bottom. Corals and crinoids crowded 
and crushed into a massive limestone on the spot where they lived 
and died, ferns and terrestrial plants matted together into a bed of 
coal where they originally grew, the scattered shells of a submarine 
sand-bank, the snails and lizards that left their mouldering remains 
within a hollow tree, the insects that have been imprisoned within 
the exuding resin of old forests, the footprints of birds and quad- 
rupeds or the trails of worms left upon former shores—these, and 
innumerable other pieces of evidence, enable the geologist to realise 
in some measure what the vegetable and animal life of successive 
periods has been, and what geographical changes the site of every 
and has undergone. 
It is evident that to deal successfully with these varied materials, 
a considerable acquaintance with different branches of science 1s 
. —l 
on a 
Fk Ge 
: t. % r 
= Roos 
ear ee 
ee Me ee ee ee 
span’ 
a 
4 
wal 
























