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                       Common Minerals and Rocks

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                   Boston Society of Natural History

                      GUIDES FOR SCIENCE-TEACHING

                                NO. XII

                       COMMON MINERALS AND ROCKS

                          BY WILLIAM O. CROSBY

                     D. C. HEATH & CO., PUBLISHERS

                       BOSTON  NEW YORK  CHICAGO




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                              _Copyright_

                BY THE BOSTON SOCIETY OF NATURAL HISTORY

                                  1881


                                 I D 2




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                             INTRODUCTION.

                             [Illustration]


Minerals and rocks, or the inorganic portions of the earth, constitute
the proper field or subject-matter of the science of Geology. Now the
inorganic earth, like an animal or plant, may be and is studied in three
quite distinct ways, giving rise to three great divisions of geology,
which, as will be seen, correspond closely to the main divisions of
Biology.

First, we may study the forces now operating upon and in the earth—the
geological agencies—such as the ocean and atmosphere, rivers, rain and
frosts, earthquakes, volcanoes, hot springs, etc., and observe the
various effects which they produce. We are concerned here with the
dynamics of the earth; and this is the great division of _dynamical
geology_, corresponding to physiology among the biological sciences.

Or, second, instead of geological causes, we may study more particularly
geological effects, observing the different kinds of rocks and of
rock-structure produced by the geological agencies, not only at the
present time, but also during past ages. This method of study gives us
the important division of _structural geology_, corresponding to anatomy
and morphology.

All phenomena present two distinct and opposite aspects or phases which
we call _cause_ and _effect_; and so in dynamical and structural geology
we are really studying the opposite sides of essentially the same
classes of phenomena. In the first division we study the causes now in
operation and observe their effects; and then, guided by the light of
the experience thus gained, we turn to the effects produced in the past
and seek to refer them to their causes.

These two divisions together constitute what is properly known as
physiography; and they are both subordinate to the third great division
of geology,—_historical geology_,—which corresponds to embryology.

The great object of the geologist is, by studying the geological
formations in regular order, from the oldest up to the newest, to work
out, in their proper sequence, the events which constitute the earth’s
history; and dynamical and structural geology are merely introductory
chapters, the alphabet, as it were, which must be learned before we are
prepared to read understandingly the grand story of the geological
record.

Our work in this short course will be limited to the first two
divisions,—_i.e._, to dynamical and structural geology. We will attempt,
first, a general sketch of the forces now concerned in the formation of
rocks and rock-structures; and after that we will study the composition
and other characteristics of the common minerals and rocks.

The scope of this work, and its relations to the whole field of geology,
are more clearly indicated by the following classification of the
geological sciences:—

                {DYNAMICAL GEOLOGY    {_Physical Geology._
                                      {_Chemical Geology._

       GEOLOGY  {STRUCTURAL GEOLOGY   {_Mineralogy._
                                      {_Petrography_ {Lithology.
                                                     {Petrology.
                {HISTORICAL GEOLOGY.

Many teachers will desire to fill in some of the details of the outline
sketch presented in this Guide, and for this purpose the following works
are especially recommended:—

    ELEMENTS OF GEOLOGY. By Prof. Joseph Le Conte. 1882. D.
        Appleton & Co., New York. Nearly 600 pages.

    MANUAL OF GEOLOGY. By Prof. J. D. Dana. Third edition. 1880.
        800 pages.

    TEXT-BOOK OF GEOLOGY. By Prof. A. Geikie. 1882. Macmillan &
        Co., London. Nearly 1000 pages.

As a reference-book for mineralogy, the following treatise is
unsurpassed:—

    TEXT-BOOK OF MINERALOGY. By Edward S. Dana. 1883. John Wiley
        & Sons, New York.

And, as an introduction to the study of minerals, and, through these, to
the study of rocks,—

    FIRST LESSONS IN MINERALS. Science Guide No. XIII. By Mrs.
        E. H. Richards.

cannot be too highly recommended. Teachers will find this little primer
of 46 pages invaluable with young children, and with all who have had no
previous training in chemistry.

As an admirable continuation of the work begun in these pages, teachers
are referred to Professor Shaler’s “First Book in Geology.” In this our
brief sketch of the geological agencies is amplified and beautifully
illustrated; and rarely have the