The Student's Manual of Geology |
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Common terms and phrases
acid action albite alumina angles appear atoms augite axis basalt beds bodies calcareous calcite called carbonate of lime Carboniferous Limestone cavities cent chalybite character chemical chlorite clay cleavage coal colour compact composition compounds contain contorted crust crystalline crystals denudation deposition depth districts dolerite dolomite dykes earth fault feet felspar felstone fissures foliation formation fracture fragments garnet Geol geological geologists gneiss grains granite gypsum horizontal hornblende hydrated igneous rocks inclined intrusive iron irregular joints land lava layers less lodes magnesia mass matter melaphyre metals metamorphic metamorphic rocks mica mica-schist miles mineral molecules occur Old Red Sandstone original orthoclase oxide planes porphyritic produced pyrites quartz reefs river salt sand shale side silicates Silurian slate sometimes stone strata stratified structure substances sulphate sulphur surface temperature texture thickness tion trachyte trap trap-rocks trappean traversed tuff valleys varies varieties veins vertical volcanic
Popular passages
Page 726 - Now, it is obvious that the shifting of the equatorial current of the Atlantic only a few degrees to the south of its present position — a thing which would certainly take place under the conditions which we have been detailing — would turn the entire current into the Brazilian branch, and instead of flowing chiefly into the Gulf of Mexico, as at present, it would all flow into the Southern Ocean, and the Gulf-stream would consequently be stopped.
Page 722 - ... small portion which falls as snow disappears in the course of a few weeks at most. But in the circumstances under consideration, the mean winter temperature would be lowered so much below the freezing-point that what now falls as rain during that season would then fall as snow. This is not all ; the winters would then not only be colder than now, but they would also be much longer.
Page 726 - Ocean, and the Gulf-stream would consequently be stopped. The stoppage of the Gulf-stream, combined with all those causes which we have just been considering, would place Europe under a glacial condition, while at the same time the temperature of the Southern Ocean would, in consequence of the enormous quantity of warm water received, have its temperature (already high from other causes) raised enormously. And what holds true in regard to the currents of the Atlantic holds also true, though perhaps...
Page 434 - But it is a fact, that the soil, notwithstanding, remains the same in quantity, or at least nearly the same, and must have done so, ever since the earth was the receptacle of animal or vegetable life. The soil, therefore, is augmented from other causes, just as much, at an average, as it is diminished by that now mentioned ; and this augmentation evidently can proceed from nothing but the constant and slow disintegration of the rocks. In the permanence, therefore, of a coat of vegetable mould...
Page 594 - In the west, great sheets of different porphyrites, with interbedded tuffs, sandstones and conglomerates, lie in the lower part of the formation, and rising in broad masses bed above bed, form that conspicuous chain of terraced heights which stretches from near Stirling through the range of the Campsie, Kilpatrick, and Renfrewshire hills, to the banks of the Irvine in Ayrshire, and thence westward by the Cumbrae Islands and Bute, to the south of Arran.
Page 421 - 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 be reduced by such a removal.
Page 721 - Now, the perihelion of the orbit is situated nearly at the place of the northern winter solstice ; so that, were it not for the compensation we have just described, the effect would be to exaggerate the difference of summer and winter in the southern hemisphere, and to moderate it in the northern ; thus producing a more violent alternation of climate in the one hemisphere, and an approach to perpetual spring in the other. As it is, however, no such inequality subsists, but an equal and impartial...
Page 414 - But, when standing beneath the base of the cliff, and in that part of the mine where but nine feet of rock stood between us and the ocean, the heavy roll of the...
Page 400 - The power of water to move bodies that are in it increases as the sixth power of the velocity of the current.
Page 422 - IN this communication, the author first calculated the probable amount of the solid matter annually brought into the ocean by rivers and other agents, in suspension and solution, and the conclusion...