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LEFT GEOLOGY 285 GEOLOGY scribe what the earth now is, geology attempts to furnish the reason why. History. — Though it was only during the 19th century that geology has started up into the vigor of manhood, yet its birth took place ages ago. Isolated geo- logical observations or hypotheses occur abundantly in ancient literature. "As for the earth, out of it cometh bread; and under it is turned up as it were fire" (Job xxviii: 5); an anticipation of the Huttonian hypothesis. Egypt, according to Herodotus, is the gift of the Nile, that is, the river brought down the silt which constitutes the fertile soil of the delta and other parts of Lower Egypt. The best geologist of antiquity was the ge- ographer Strabo, who lived in the 1st century a. d. Modern geology began with Werner, who was a professor in the School of Mines at Freiberg, in Saxony, in 1775. He believed that a series of universal formations had been deposited in succession from a chaotic fluid. Basalt was supposed to have had the same origin, but to this view various conti- nental observers were opposed. Hutton published in 1788 his "Theory of the Earth," developed in a separate work m 1795, He assumed no causes but those now existing. He showed that geology and cosmogony were different. "In the economy of the world," he said, "he could find no trace of a beginning, no prospect of an end." He held basalt, granite, etc., to be of igneous origin. The Wei-nerians were called Neptunists, their opponents Vulcanists. In 1798 Cuvier published his "Fossil Bones," which gave a great impulse to palaeontology. Forces or Causes in Operation. — After inquirers had outgrown the belief in fos- sils produced by the plastic power of nature or all entombed simultaneously by the Noachian deluge, the belief vfas entertained that there had been a series of creations and catastrophies, the latter causing the universal destruction of all pre-existing species. The belief was also entertained that some external causes, say the forces producing earthquake and volcanic action, were more potent in former times than now. This Professor Huxley calls catastrophism, which he defines to be any form of geological speculation which, in order to account for these phenomena, supposes the opera- tion of forces different in their nature or immeasurably different in power from those which are at present in action in the universe. The second school of geology is that called by Huxley uniformitarianism. This looks only to causes now in opera- tion for the explanation of geological phenomena. Of this school Hutton was the founder, though it was Sir Charles Vol. IV — Cyc— S Lyell that carried it forward to triumph. He showed the enormous changes which the causes now in operation are still pro- ducing, and that nearly every phenom- enon, attributed to abnormally potent causes acting suddenly and briefly, could be produced by causes not more intense than those in action now, but operating through immense periods of bygone time. In his ''Principles of Geology," he ex- amines aqueous causes, the action of water acting in connection with tides, currents, etc., in seas, rivers, and lakes, also the action of ice in all its forms. Next he inquires into igneous causes, volcanoes, and earthquakes. Climate and organic life are also carefully investi- gated in the work. The doctrine of the third school of geologists is called by Professor Huxley evolutionism; it accepts nearly the whole of uniformitarianism, except the part referring to the development of organic life. In his later years Sir Charles Lyell became an evolutionist. See Darwinian Theory: Evolution. Geologic Time. — Both the uniform- itarian and the evolutionist believe that they may draw to any extent on what may be called the bank of time, which will be found "ready to discount any quantity of hypothetical paper." Sir William Thompson holds that any such drafts must be limited "within some such period as 100,000,000 years"; and another natural philosopher considers the time at call only about 60,000,000 years. Huxley believes the necessity for these limitations is not proved, though perhaps one, two, or three hundred mil- lions of years might be enough to ac- count for geological phenomena. With regard to the subdivision of the time, long or short, at the gelogists' command, the sedimentary strata having been laid down by water, the relative thickness of each stratum will measure the proportion of geologic time required for its deposition. Geologic strata. — The geological rec- ord is made up as follows, beginning with the five great PERIODS. 5. Quaternary. The age of man. 4. Cenozoic Period. Age of Mammals. 3. Mesozoic Period. Age of Reptiles. Age of Coal 2. Palaeozoic Period. Period. Plants. Age of Fishes. Age of Inver- tebrates. Lifeless and 1. Archaean dawn of life. The following list gives the eras to- gether with their dependent series and sub-divisions in descending order: