We thus see, according to the grand views of Elie de Beaumont,
how chains of mountains dividing different climates and floras and different
races of men, reveal to us their 'relative age', both by the character of
the sedimentary strata they have uplifted, and by the directions which they
follow over the long fissures and which the earth's crust is furrowed.
Relations of superposition of trachyte and of syenitic porphyry, of diorite
and of serpentine, which remain in the rich platinum districts of the Oural,
and on the south-western declivity of the Siberian Alti, are elucidated by
the observations that have been made on the plateaux of Mexico and
Antioquia, and in the unhealthy ravines of Choco. The most important facts
on which the physical history of the world has been based in modern times,
have not been accumulated by chance. It has at length been fully
acknowledged, and the conviction is characteristic of the age, that the
narratives of distant travels, too long occupied in the mere recital of
hazardous adventures, can only be made a source of instruction where the
traveler is acquainted with the condition of the science he would enlarge,
and is guided by reason in his researches.
It is by this tendency to generalization, which is only dangerous in its
abuse, that a great portion of the physical knowledge already acquired may
be made the common property of all classes of society; but, in order to
render the instruction impaired by these means commensurate with the
importance of the subject, it is desirable to deviate as widely as possible
from the imperfect compilations designated, till the close of the eighteenth
century, by the inappropriate term of 'popular
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knowledge.
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