THE ELEMENTS OF GEOLOGY





INTRODUCTION

THE SCOPE AND AIM OF GEOLOGY


Geology deals with the rocks of the earth's crust. It learns from
their composition and structure how the rocks were made and how
they have been modified. It ascertains how they have been brought
to their present places and wrought to their various topographic
forms, such as hills and valleys, plains and mountains. It studies
the vestiges which the rocks preserve of ancient organisms which
once inhabited our planet. Geology is the history of the earth and
its inhabitants, as read in the rocks of the earth's crust.

To obtain a general idea of the nature and method of our science
before beginning its study in detail, we may visit some valley,
such as that illustrated in the frontispiece, on whose sides are
rocky ledges. Here the rocks lie in horizontal layers. Although
only their edges are exposed, we may infer that these layers run
into the upland on either side and underlie the entire district;
they are part of the foundation of solid rock which everywhere is
found beneath the loose materials of the surface.