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. | |||||||||
| 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.