crystals and will take a polish, while
ordinary uncrystallized limestone will not. The igneous rocks are
chiefly granite; and granite is formed of orthoclase-feldspar, mica, and
quartz. (The word "orthoclase" means straight fracture, and the
orthoclase-feldspar has two lines of cleavage at right angles to each
other.) This is the ordinary composition of granite, but there are a
great many variations, chiefly as to color and proportions of the
ingredients named.

The igneous rocks, then, are the lowest of all; then come the
metamorphic rocks; and as before stated, on top of metamorphic rock
begins the first evidence of life in its lowest form. The Paleozoic
(ancient life) or Primary period is made up of a number of subdivisions.
The first and oldest division is called the "Silurian" age, which is
underlaid by the metamorphic rocks and overlaid by the rocks of the
Devonian period. It is called Silurian, from the name of a kind of fish,
fossils of which are found in the rocks of this age, which are
distinguished for the absence of land-plant fossils and vertebrate
animals.

In the Silurian strata are found limestones, slate, flagstones, shales,
etc. On top of the Silurian begins the "Devonian" age, in which is found
the old red sandstone, as well as limestone and slate; and here begin to
be found the fossils of land-plants. On top of the Devonian lies the
"Carboniferous" series, which complete the series of the primary period.
In the lower part of this stratum is found carboniferous limestone,
which is overlaid by a kind of stone called millstone grit, and on top
of this lie the true carboniferous strata or coal-bearing measures. In
the coal strata are found the first reptile fossils.

On top of the coal measures begins the Secondary period, or "Mesozoic"
(middle life). This period is distinguished for the great development of
reptiles, and is called the "age of reptiles." In this age occur the
first traces of mammals, and birds, and fishes with bony skeletons.
Among plants we find here the first evidence of palms. The formation is
chiefly chalk, sandstones, clays, limestone, etc. We now come to the
last or "Tertiary" period, which brings us to the top earth. This is
chiefly formed of sedimentary rocks--those which have been formed by
the settling of sediment, in water.

While we are forced to these general conclusions in regard to the
building of the world, and to its subsequent distortion by the series of
upheavals