THE FIELD NATURALIST'S KNOWLEDGE. 53
And turning our eyes away from these grander scenes of Nature
to the smaller but most beautiful results of its unseen working, we
see the exquisite forces produced by molecular movements and
re-arrangements in the crystals of the mineral kingdom. Nor is the
accompanying additional result of molecular re-arrangement less
beautiful, the crystalline texture, as seen in the sparkling diamond,
the brilliant ruby, or the splendid sapphire. And although in
English field-work we do not meet with these princes of the mineral
kingdom, we frequently find in situ or in the pebbles of the sea-shore
the pellucid rock-crystal, the varied formed calcite, and, especially in
the London Clay districts of East Anglia, the often quite transparent
selenite.
But crystallization is not by any means always on such a small scale
in geology as this. It plays a most important part in the formation,
and especially in the conservation of great rock masses, which
through it are rendered hard and enduring, and so form lofty
eminences or bold headlands instead of lowly valleys and receding
coast lines. And again in ordinary so-called metamorphism when
rocks have been changed in character, and been hardened by heat
and pressure, and even by pressure alone, we are reminded of the
great part played in geology by the physical forces of the inorganic
world. Nay, too, even in the commonest of all geological phe-
nomena, denudation and transportation by water action, and
separation and deposition of new rock-forming materials, there is a
conspicuous display of the mechanical forces, and we see that vis-
inertia, gravitation and momentum, are the determining causes of
those results the study of which forms the chief portion of geological
science. Not only have Himalayan summits and Alpine peaks,
Andean Cordilleras and Iberian sierras, been fashioned by the forces
of inorganic nature, but the Chalk Downs of Kent and Sussex, and
the London Clay elevations of Essex and Middlesex, have also
received their beautiful slopes and smooth roundings from the action
of the same all-pervading and never-tiring forces. The materials,
too, of these mountains and hills, to a very large extent, as well as
those of the ground over which we now stand, have likewise been
accumulated by the mechanical forces inherent in inorganic matter.
And not only has a large proportion of the material forming the
dry land been accumulated by mechanical forces, but it has been
made to appear above the waters by those forces also. The slow and
silent upward or downward movement of large areas of the earth's