: The Elements of Geology by Norton William Harmon - Geology Geology

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INTRODUCTION.--THE SCOPE AND AIM OF GEOLOGY

PART I

EXTERNAL GEOLOGICAL AGENCIES

PART II

INTERNAL GEOLOGICAL AGENCIES

HISTORICAL GEOLOGY

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.

The successive layers of the rock suggest that they were built one after another from the bottom upward. We may be as sure that each layer was formed before those above it as that the bottom courses of stone in a wall were laid before the courses which rest upon them.

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