Elements of geology : a text-book for colleges and for the general reader / by Joseph Le Conte.

  • Joseph LeConte
Date:
1898,
Catalogue details

Licence: Public Domain Mark

Credit: Elements of geology : a text-book for colleges and for the general reader / by Joseph Le Conte. Source: Wellcome Collection.

    24/698 page 2
    « geognosy. 2. Dynamical geolofiy, or pliysical and chemical geology. 3. Historical geology^ or the history of the earth. But there are two important points of difference between geology and organic science. The central department of organic science is pliysiology, and both anatomy and embryology are chiefly studied to throw light on this. But the central department of geology, to which the others are subservient, is history. Again: in case of organisms —especially animal organisms—the nature of the changes producing development is such that the record of each previous condition is suc- cessively and entirely obliterated; so that the science of embryology is possible only by direct observation of each successive stage. If this were true also of the earth, a history of the earth would, of course, be impossible. But, fortunately, we find that each previous condition of the earth has left its record indelibly impressed on its structure. Order of Treatment.—The prime object of geology is to determine the history of the earth, and of the organisms which have successively inhabited its surface. The structure and constitution of the earth are the materials of this history, and the physical and chemical changes now going on around us are the means of interiKcting this structure and constitution. Evidently, therefore, the only logical order of pre- senting the facts of geology is to study, first, the causes, physical and chemical, noio in operation and producing structure ; then the structure and constitution of the earth which, from the beginning, have been produced by similar causes; and, lastly, from the two preceding to un- fold the history of the earth. Geology may be defined, therefore, as the history of the earth and its inhabitants, as revealed in its strticture, and as interpreted by causes still in operation.* There is no other science which requires for its full comprehension a general knowledge of so many other departments of science. A knowledge of mathematics, physics, and chemistry, is required to under- stand dynamical geology; a knowledge of mineralogy and lithology is required to understand structural geology; and a knowledge of zoology and botany is required to understand the affinities of the animals and plants which have successively inhabited the earth, and the laws which have controlled their distribution in tiine. * The great importance of studying causes now in operation as a basis of scien- tific geology was first brought out by llutton, but it was through the writings of Sir Charles Lyell that it became generally iicueptod.
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