which are caused by the forces operating in and on this sphere. Of all
the chapters of this great story, that which relates to the history of
the work done by the heat of the sun is the most interesting and
awakening. Therefore an effort has been made to present the great
successive steps by which the solar energy acts in the processes of
the air and the waters.

The interest of the beginner in geology is sure to be aroused when he
comes to see how very far the history of the earth has influenced the
fate of men. Therefore the aim has been, where possible, to show the
ways in which geological processes and results are related to
ourselves; how, in a word, this earth has been the well-appointed
nursery of our kind.

All those who are engaged in teaching elementary science learn the
need of limiting the story they have to tell to those truths which can
be easily understood by beginners. It is sometimes best, as in stating
such difficult matters as those concerning the tides, to give
explanations which are far from complete, and which, as to their mode
of presentation, would be open to criticism were it not for the fact
that any more elaborate statements would most likely be
incomprehensible to the novice, thus defeating the teacher's aim.

It will be observed that no account is here given of the geological
ages or of the successions of organic life. Chapters on these subjects
were prepared, but were omitted for the reason that they made the
story too long, and also because they carried the reader into a field
of much greater difficulty than that which is found in the physical
history of the earth.