Text-book of Geology |
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Common terms and phrases
abundant accumulation acid alteration augite basalt beds Bull calcareous calcite carbonate Carboniferous cavities character chemical clay compact cone consist constituents containing crystalline rocks crystals denudation deposits depth detritus diabase diorite dykes earth earth's crust Edin eruptive rocks evidence feet felsite felspar fissures foliated formations fossils fragments Géol geological geologists glacier glass globe gneiss grains granite heat hornblende igneous rocks iron Jahrb Journ lakes land lava layers less leucite lime limestone magnetite mass materials metamorphism mica Michel-Lévy microscope miles minerals molten mountain observed occur ocean olivine organic original orthoclase oxide Palæozoic plagioclase plants porphyritic portions postea present probably Proc pyroxene Q. J. Geol quartz regions rise river round sand sandstone schistose schists Section sediment sedimentary shales shells silicates Silurian solid sometimes strata stratified structure substance surface temperature terrestrial thick traced trachytes tuffs vapour veins vitreous weathering
Popular passages
Page 16 - ... the Polar regions must have been ever rising and the equatorial ones falling ; but, as the ocean always followed these changes, they might quite well have left no geological traces.
Page xiii - But it ought not to be allowed a firmer footing, nor on any account be suffered to blind us to the obvious truth that the few centuries, wherein man has been observing nature, form much too brief an interval by which to measure the intensity of geological action in all past time. For aught we can tell, the present is an era of quietude and slow change, compared with some of the eras that have preceded it.
Page 752 - tilestones ' by Murchison, and, being often red in color, were included by him as the base of the Old Red Sandstone, into which they gradually and conformably ascend. They point to a gradual change of physical conditions, which took place at the close of the Silurian period in the west of England and brought in the peculiar deposits of the Old Red Sandstone. There is every reason to believe that for a long time the marine sedimentation of Upper Silurian type continued to prevail in some areas, while...
Page 462 - plain of marine denudation ' is that sea-level to which a mass of land had been reduced mainly by the subaerial forces, the line below which further degradation became impossible, because the land was thereafter protected by being covered by the sea. Undoubtedly the last touches in the long process of sculpturing were given by marine waves and currents, and the surface of the plain, save where it has subsided, may correspond generally with the lower limit of wave action.
Page 650 - At the present day, for example, the higher fauna of Australia is more nearly akin to that which flourished in Europe far back in Mesozoic time than to the living fauna of any other region of the globe.
Page 459 - before the sea, advancing at a rate of ten feet a century, could pare off more than a mere marginal strip of land between 70 and 80 miles in breadth, the whole land might be washed into the ocean by atmospheric denudation...
Page 452 - the mere consideration of the number of cubic feet of detritus annually removed from any tract of land by its rivers does not produce so striking an impression upon the mind as the statement of how much the mean surface level of the district in question would...
Page 49 - A very slight deviation of the inner surface of the shell from perfect sphericity would suffice, in virtue of the quasi-rigidity due to vortex motion, to hold back the shell from taking sensibly more precession than it would give to the liquid, and to cause the liquid (homogeneous or heterogeneous) and the shell to have sensibly the same precessional motion as if the whole constituted one rigid body.
Page 517 - An important feature of these joints, as mentioned by this authority, is the direction in which they intersect each other. In general they have two dominant trends, one coincident on the whole with the direction in which the strata are inclined from the horizon, and the other running transversely at a right angle, or nearly so. The first are called "dip joints
Page 605 - The second hypothesis supposes that the elements of these various rocks were originally deposited as, for the most part, chemically formed sediments, or precipitates ; and that the subsequent changes have been simply molecular, or, at most, confined in certain cases to reactions between the mingled elements of the sediments, with the elimination of water and carbonic acid.