other
before they discovered that it was made of both. So prone are men to
hug their theories and shut their eyes to any antagonistic facts, that
it is related of Werner, the great leader of the Aqueous school, that
he was actually on his way to see a geological locality of especial
interest, but, being told that it confirmed the views of his
opponents, he turned round and went home again, refusing to see what
might force him to change his opinions. If the rocks did not confirm
his theory, so much the worse for the rocks,--he would none of them.
At last it was found that the two great chemists, fire and water, had
worked together in the vast laboratory of the globe, and since then
scientific men have decided to work together also; and if they still
have a passage at arms occasionally over some doubtful point, yet the
results of their investigations are ever drawing them nearer to each
other,--since men who study truth, when they reach their goal, must
always meet at last on common ground.

The rocks formed under the influence of heat are called, in geological
language, the Igneous, or, as some naturalists have named them, the
Plutonic rocks, alluding to their fiery origin, while the others have
been called Aqueous or Neptunic rocks, in reference to their origin
under the agency of water. A simpler term, however, quite as
distinctive, and more descriptive of their structure, is that of the
stratified and massive or unstratified rocks. We shall see hereafter
how the relative position of these two classes of rocks and their
action upon each other enable us to determine the chronology of the
earth, to compare the age of her mountains, and, if we have no
standard by which to estimate the positive duration of her continents,
to say at least which was the first-born among them, and how their
characteristic features have been successfully worked out. I am aware
that many of these inferences, drawn from what is called "the
geological record," must seem to be the work of the imagination. In a
certain sense this is true,--for imagination, chastened by correct
observation, is our best guide in the study of Nature. We are too apt
to associate the exercise of this faculty with works of fiction, while
it is in fact the keenest detective of truth.

[Illustration: DIKES.]

Besides the stratified and massive rocks, there is still a third set,
produced by the contact of these two, and called, in consequence of
the changes thus brough