Ice Ages, Recent and AncientMacmillan, 1926 - 296 páginas |
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Términos y frases comunes
ancient Antarctica Archæan arctic Australia beneath boulder beds boulder clay boulder conglomerate breccia Cambrian Carboniferous coal Cobalt cold continents covered described Devonian drift earth enclosed Europe evidence feet thick flora formation formed fossils Gangamopteris Geol geological geologists glacial beds glacial deposits glacial origin glacial periods glaciers glomerate Glossopteris granite Greenland heat Huronian ice action ice age ice sheet India interglacial interglacial beds interglacial periods islands Jour Keewatin kilometers known Labrador sheet Lake late Pre-cambrian limestone lower marine matrix mentioned meters mild climate moraines mountain glaciers North America northern occur Ordovician outcrops Paleozoic pebbles Permian Permo-carboniferous glaciation plants Pleistocene Pleistocene ice Pre-cambrian present probably quartzite reached region reptiles River rocks sandstone sea level seasonally banded shales Silurian slate South Africa southern southwest stratified striæ striated stones striated surface subangular suggested Talchir temperature theory tillite tion tropical valley varve warm weathering
Pasajes populares
Página 270 - ... or stratosphere, since, from whatever point of introduction, the winds of the upper atmosphere would soon spread it more or less evenly over the entire earth. A little calculation shows, too, that this quantity of dust yearly, during a period of 100,000 years, would produce a layer over the earth only about half a...
Página 254 - ... the inclination of the earth's axis to the plane of the ecliptic, and more remotely upon the variations in that inclination known as precession and nutation.
Página 180 - This conglomerate is at least 700 or 800 feet in thickness, and consists dominantly of a firm, somewhat dense, finely textured, reddish, argillaceous matrix, in which are embedded angular to subangular pebbles and boulders ranging in size from microscopic to 3 or 4 feet in diameter. The matrix appears to have approximately the composition of a boulder clay, and the greater number of the pebbles and boulders are composed of limestone or dolomite, but some were noted composed of other sediments such...
Página 272 - As has been mentioned, the time shown by a sundial is called Apparent Solar Time. It differs from Mean Solar Time by an amount known as the Equation of Time, which is the total effect of two causes which make the length of the apparent solar day nonuniform. One cause of variation is that the orbit of the Earth is not a circle, but an ellipse, having the Sun at one focus.
Página xxii - these short spells of trial and stress meant far more for the development of the world's inhabitants than all the long periods of ease and sloth when the earth was a hothouse." He adds that, "it may be that the races of civilized men are merely evanescent phenomena bound up with the bracing climate of a brief ice-age, to sink, after a few more thousand years, into a state of tropical sloth and barbarism when the world shall have fallen back into its usual relaxing warmth...
Página 213 - Howchin, the tillite consists "mainly of a groundmass of unstratified, indurated mudstone, more or less gritty, and carrying angular, subangular, and rounded bowlders (up to 11 feet in diameter), which are distributed confusedly through the mass. It is in every respect a characteristic till
Página 115 - Umzinto rivers the boulder-bearing clay passes into beds which very nearly simulate the condition of true slate, but have their lines of cleavage in the direction of, instead of transverse to, the general stratification.
Página 10 - ... parts remains unchanged." And he goes on to remind the reader that : — " At present the climate of eastern North America is cooler than that of the corresponding parts of Europe. Arctic conditions prevail on the Labrador coast down to latitudes which in Europe include Christiania, Glasgow, Edinburgh and London, where the winters are comparatively mild. The Labrador coast is treeless and has eight or nine months of winter just across the Atlantic from the south of Scotland where the laurel and...
Página xxiii - ... of trial and stress meant far more for the development of the world's inhabitants than all the long periods of ease and sloth when the earth was a hothouse." He adds that, "it may be that the races of civilized men are merely evanescent phenomena bound up with the bracing climate of a brief ice-age, to sink, after a few more thousand years, into a state of tropical sloth and barbarism when the world shall have fallen back into its usual relaxing warmth and moisture, the East African conditions...
Página 207 - bowlders reaching diameters of 3 feet 8 inches, having grooves like glacial striae, in a conglomerate with sandy matrix belonging to the Keweenawan of Pointe aux Mines, near the southeast end of Lake Superior. Messrs. Lane and Seaman describe a Lower Keweenawan conglomerate as containing 'a wide variety of pebbles and large bowlders, in structure at times suggestive of till,' from the south shore of Lake Superior