99 CHAPTER IV. GEOLOGY. I. INTRODUCTION. Or what does Geology treat? Its object is to examine and describe the Crust of the To what sort of fruit may you compare our Globe? How does it resemble an orange in shape? In its being a slightly flattened sphere. Of what, as to its make, is an orange composed? What likeness is there between this and the earth? Of what does the central part consist? of unknown incandescent or molten materials. Of what does the Crust consist? Of those materials which Geology examines. Of what does Geology inform us? 1. Of what materials the crust consists. 2. Of the order in which they are arranged. 3. Of changes effected in their position or condition by mechanical or chemical agency. 4. Of organic bodies (or fossils) found in inorganic materials. 5. Of the particular benefit to be derived from knowing these facts. What would a geologist be able to tell us? 1. The mineral character of a stratum. 2. Its subdivisions, thickness, and extent. 3. Its mode of formation, and its characteristic fossils. 5. The rise of springs, metalliferous productions, &c. What is the thickness of the earth's crust? 1. The stratified and unstratified crust is accounted to be about ten miles thick: that is, it would be so if all strata lay on those immediately before them. But, 2. The depth at which all things are in a state of fusion is more than fifty miles. What portion of the earth's radius is the stratified crust? 4000400th part of it. 10 = Of what is the earth's crust composed? Of a series of stratified and unstratified beds or layers, composed of various substances. What are these substances? Chiefly earths, and alkalies, rocks, and minerals. Mention four compounds which may be said to constitute the solid crust of the globe. 1. Siliceous: Sand, Sandstone, Grauwacke, Quartz Rock. 2. Argillaceous: Alluvial Clay, Laminated Clay, Slaty Shale, Clay-Slate. 3. Calcareous: Marl, Chalk, Lime Stone, Crystalline Marble. 4. Carboniferous: Peat, Lignite, Brown Coal, Common Coal. (The gradation in each of these four lines is from the surface of the earth downwards; that is from the Tertiary to the Primary.) What is the cultivated surface of the earth called? Vegetable soil; and next under it is Subsoil. What is Subsoil? It is derived from the decomposition of the subjacent rocks. What lies under this double kind of surface? That which properly forms the Crust. How do we divide it? Into Unstratified and Stratified Rocks. Must this distinction be kept in mind? What is our first assertion with regard to Creation? Quote St. Paul on this point: Heb. xi. 3. "Through faith we understand that the worlds were framed by the word of God, so that things which are seen were not made of things which do appear." What may you suppose the first state of our globe to have been? Fluid from intense heat. How did it become solid? By the radiation of heat from its surface into space. What would follow from this? The particles of matter would approximate and crystallize. What would be the first result of this? The formation of a shell or crust composed of oxidated metals and metalloids, constituting various rocks of the granitic series, around an incandescent nucleus. From what have the materials of the Stratified rocks been derived? In a great measure perhaps from the detritus of the Unstratified crystalline rocks. What causes have been instrumental in producing the actual condition of the surface of our globe? Do 1. The passing of the unstratified crystalline rocks from a fluid to a solid state. 2. The deposition of stratified rocks at the bottom of ancient seas. 3. The elevation of both sorts of rocks from beneath the sea at successive intervals, so as to form continents and islands. 4. Violent inundations, and the decomposing power of atmospheric agents, producing partial destruction of those lands, and forming from their detritus, extensive beds of gravel, sand, and clay. 5. Volcanic eruptions. you view the formation of the earth's crust as being strictly a Creation? I view it rather as the result of the various changes of previously created materials. What do you say of these changes? They were, on the part of the Almighty Creator and Disposer of all things, the preparation of the globe as the dwelling-place of Man. What may you suppose the first state of the earth to have been? A globe or sphere with a smooth or even surface. What do you then suppose to have taken place? An elevation, and therefore a disruption, of the surface by volcanoes, earthquakes, &c. What was produced by this heaving process? The Fundamental or Primary Rocks. What followed after this? These rocks being worn, broken, decomposed, &c. by various agents, there would be an overspreading deposit, with different productions. What productions do you mean? |