trials, resulting only in disappointment, the students of rocks followed the example of the theologians; and, in lieu of observations and facts, produced only the useless and often virulent polemics of the Neptunist and Vulcanist.
Again, there was a reaction against such waste of energy. Geologists, wearied by more barren controversy, turned eagerly to some new field where observation should be less difficult. They had opened the great book of Nature and had first tried to read the text; but the hieroglyphics were obscure, and the clew could not be found. Is it strange, therefore, that they should have gladly left this hard and unintelligible writing for the picture-book which Nature spread before them in the fossils? Here at least was something tangible. None now doubted that these fossils had once been living organisms which could be understood by careful comparison with living forms.
It was through the study of fossil organisms—or paleontology—that geology first accomplished its true aim, viz., the deciphering of a portion of the earth's history by observed facts. We can hardly wonder that a field so fruitful should, since the beginning of our century, have been cultivated to the exclusion of almost every other. But paleontology is essentially a biological, not a geological science. Its service to the sum of human knowledge can scarcely be overestimated, for it has done much in establishing the greatest generalization of this or perhaps of any century—the doctrine of evolution. Nevertheless, its contributions must ever be to the history of life on the globe, rather than to the history of the life of the globe.
So strong has been the growth of the organic side of our science that a popular idea still prevails that there is no geology aside from stratigraphy and the fossil-bearing rocks. The paleontological school is still in the ascendant, but it is no longer without a vigorous rival.
Within recent years there seems to have been infused into almost every domain of physical science a fresh life. Through gradually acquired generalizations higher points of view have been reached; old notions have been discarded for newer and broader ones. Prof. Langley tells us of the "new astronomy"; the doctrine of the conservation of energy has given us a new physics; evolution, a new biology; and the study of carbon compounds, a new chemistry. So, too, the application of the microscope to the study of rocks has given us a new geology.
The recent development in the science of the earth consists of the return to the work begun by its earliest pioneers. The old Petrographers were right. If we would know the life-history of our planet, we must learn the origin, structural relations, and composition of our rocks. We must discover the forces—chemi-
