Geology for Students and General Readers: Physical geology ... |
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Common terms and phrases
accumulations acid action Alumina angles Augite Basalt beds beneath called Carbonate of Lime carried cause character chemical Clay clayey cleavage Coal coarse composition contain contortion Coral Crystalline rocks crystals density deposits Diorite dissolved Dolomite earth earth's crust explanation fact fault Felsite Felspar Felstone fluid foliation formation formed Geol geologists Geology give rise glacier glassy Gneiss gradually grains Granite Gritstone ground hard heat hills Hornblende instance Journ lakes land lava layers Limestone Magnesia marine mass matter Metamorphic Rocks metamorphism Mica mineral moraines mountain chains occur Oligoclase origin Orthoclase planes Porphyritic portions present pressure prism produced Quartz reef result rhombohedron ridge river sand Sandstones sandy Sanidine Schist sediment Shales shape side Silica slope solid sometimes stones strata streams structure subaërial substances surface Syenite temperature texture thickness thin tion Trachyte Triclinic valley varieties volcanic
Popular passages
Page 223 - In the plain of S. Lio, a fissure six feet broad and of unknown depth opened with a loud crash, and ran in a somewhat tortuous course to within a mile of the summit of /Etna, traversing a length of twelve miles, and emitting a most vivid light.
Page 116 - ... of univerfal decay and degradation, which may be traced over the whole furface of the land, from the mountain top to the fea fhore. That we may perceive the full evidence of this truth, one of the moft important in the natural hiftory of the globe, we will begin our furvey from the latter of...
Page 142 - look and a brownish colour, and become more and more mixed with a fine amorphous redbrown powder, which increases steadily in proportion until the lime has almost entirely disappeared. This brown matter is in the finest possible state of subdivision, so fine that when, after sifting it to separate any organisms it might contain, we put...
Page 272 - Ann's chapel, on the river Ogwen. So closely does the matrix of the altered rock resemble the adjoining typical porphyry in colour, texture, and even in porphyritic character, and by such insensible gradations do they melt into each other, that the suspicion or rather the conviction constantly recurs to the mind that the solid porphyry itself is nothing but the result of the alteration of the stratified masses carried a stage further into the region of that kind of absolute fusion that in so many...
Page 282 - Sedgwick describes the planes of cleavage, as ' coated over with chlorite and semi-crystalline matter, which not only merely define the planes in question, but strike in parallel flakes through the whole mass of the...
Page 523 - middle path," not generally safest in scientific speculation, seems to be so in this case. It is probable that hypotheses of grand catastrophes destroying all life from the earth, and ruining its whole surface at once, are greatly in error ; it is impossible that hypotheses assuming an equability of sun and storms for 1,000,000 years can be wholly true.
Page 4 - Hutton's first principle was that " no powers are to be employed that are not natural to the globe, no action to be admitted of except those of which we know the principle, and no extraordinary events to be alleged in order to explain a common appearance.
Page 146 - These red bands vary in thickness from a few inches to two or three feet, and...
Page 337 - Works, i. 432. ing of the present ruin ; was again let down till the sea rose at least some twenty feet above the pavement of the temple ; was again raised into dry land, and is now slowly sinking again.* Then again we have the case of the Scandinavian peninsula, where there is good reason to believe that within the memory of man the northern part of the country has been rising, perhaps at the rate of...
Page 157 - ... must be so exactly that of Till, that nearly all geologists are now agreed to look upon the latter as having been formed by the grinding and wearing away by an ice-sheet of the ground on which it rested " (p. 264). But as far as evidence from Greenland is available it throws as little light on the origin of Boulder-clay as the Swiss valleys. Thus Nordenskiold describes an area lately left by the ice as containing no moraines, and in his description makes...