mate length of time
required for the construction of sedimentary rocks like those which
natural agencies are producing to-day, there are few definite facts to
guide speculation as to the mode or duration of the process by which the
first hard crystalline surface of the earth was formed. But palaeontology
does not care so much about the earliest geological happenings, for it is
concerned with the manifold animal forms that arose and evolved after life
appeared on the globe. Questions as to the way life arose, and as to the
earliest transformations of the materials by which the earth was first
formed are not within the scope of organic evolution, although they relate
to intensely interesting problems for the student of the process of cosmic
evolution.

According to the account now generally accepted, the original material of
the earth seems to have been a semi-solid or semi-fluid mass formed by the
condensation of the still more fluid or even gaseous nebula out of which
all the planets of the solar system have been formed and of which the sun
is the still fiery core. As soon as the earth had cooled sufficiently its
substances crystallized and wrinkled to form the first mountains and
ridges; between and among these were the basins which soon filled with the
condensing waters to become the earliest lakes and oceans. The wear and
tear of rains and snows and winds so worked upon the surfaces of the
higher regions that sediments of a finer or coarser character like sand
and mud and gravel were washed down into the lower levels. These sediments
were afterwards converted into the first rocks of the so-called stratified
or sedimentary series, as contrasted with the crystalline or plutonic
rocks like the original mass of the earth and the kinds forced to the
surface by volcanic eruptions. Later the earth wrinkled again in various
ways and places so that new ridges and mountains were formed with new
systems of lakes and oceans and rivers; and again the elements continued
to erode and partially destroy the higher masses and to lay down new and
later series of sedimentary rocks upon the old.

It seems scarcely credible that the apparently weak forces of nature like
those we have mentioned are sufficiently powerful to work over the massive
crust of the earth as geology says they have. Our attention is caught, as
a rule, only by the greater things, like the earthquakes at San Francisco
and Valparaiso, and the tidal waves and cyclones o