er that it was made of
silver, and almost killing each 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 Aqueons 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 unstratified or massive rocks. We shall see hereafter how
the relative position of these two kinds of rocks and their action upon
each other enables 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 successively 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.

Beside the stratified and unstratified rocks, there is still a third
set, produced by the contact of these two, and called, in consequen