Page:Popular Science Monthly Volume 41.djvu/85

Rh stratified, and packed with, the remains of living beings, have been transformed into slates, schists, and other crystalline rocks, and the inquiry, how this has been done, can only be answered by the geologist.

5. During the process of mountain-building the earth's crust has been uplifted, shattered, or dislocated, and finally permeated by hot springs, and the cracks and rents extending to the surface filled with the precious minerals. Certainly there is good reason why we should know how the ores thus came to be brought up from the bowels of the earth and almost laid at our doors. Theoretical geology gives us the probable explanation.

6. Our North American continent has had a beginning, has passed through a period of infancy, youth, and maturity; the mountain-ranges bounding it are of different ages; its varying climates have become gradually established, and at different epochs it was fitted for the maintenance of quite different assemblages of plants and animals. The intimate relationship between these successive plant and animal worlds and the ground on which they were born, flourished, and died is now tolerably well understood by our geologists.

7. Coal and coal-oils are geological products. Geologists can now give a satisfactory account of just how coal-beds have been formed from vast peat swamps; why great beds of iron ore are interstratified with the coal. We have only had our attention drawn to coal-oils since 1860, but already our geologists feel confident that they are due to the immense profusion of marine animals or vegetables, or both, during the times before and since the great Coal period; and chemical geologists nearly all agree in believing that petroleum is due to the storage in the earth of the chemical products derived from the tissues and oily matters once forming part of the bodies of myriads of living beings.

8. It is interesting to know, and history-classes learn, the mode of origin of the people of Greece, of Rome, of the making of Great Britain, the mode of origin of the French or German peoples, and the successive steps in the history of our own nation. It is equally important to know when the worms, ascidians, early vertebrates, and fishes made their appearance; when it became possible for air-breathing vertebrates to exist, and when the forerunners of mammals and man, the amphibians, were evolved from the ganoids. Paleontology throws light on these points, if intelligently studied and properly taught.

9. Much time is given in our schools to the memorizing of the dates of the birth and death of kings and of dynasties. Why should not the pupil also learn the geological date of the first known appearance of mollusks, star-fishes, worms, insects, fishes, reptiles, birds, and beasts? There are a great many isolated