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alluvium Ammonites angle appear basin beds bone Brachiopoda Caithness calcareous carbonate Carboniferous character clay cleavage coal coal-measures coast cone conglomerate Crag crater Crocodilia crystalline deposits described Devonian diameter Diprotodon dolomites drift edge Elgin eruption Etna Eurypterus feet formation fossil fragments genera genus Geol Geological geologists gneiss granite hills inch joints Journ lava lime limestone Loch London Clay Lower Silurian Lyell Macropus margin masses memoir miles mineral molar mountain nearly noticed Nototherium observed occur Old Red Sandstone Oolitic outer palaeozoic Permian plants plates portion posterior present probably Prof quarry Quart quartz-rock R. I. Murchison ramus remains resemblance ridge river rocks sand schists Scotland scutes seen shales shells side siliceous Silurian skull slates slopes Society species specimens Stagonolepis strata stratified structure surface teeth Tertiary thick tion transverse upper valley veins volcanic Wales Zygomaturus
الصفحة 640 - ... have swept away, but which the most gentle inundations or even heavy rains could scatter in layers over the surface, where they gradually became imbedded in a mass of roots, fallen leaves, and herbaceous plants. " 4. The rate of accumulation of coal was very slow. The climate of the period, in the northern temperate zone, was of such a character that the true conifers show rings of growth not larger or much less distinct than those of many of their modern congeners...
الصفحة 639 - I have found specimens which show that in the coal-seams themselves true woody tissues have sometimes been imbedded unchanged, and converted into structureless coal, forming, like the coniferous trees converted into jet in more modern formations, thin bands of very pure bituminous material. The proportion of woody matter in this state differs in different coals, and is probably greatest in those which show the least mineral charcoal ; but the alteration which it has undergone renders it almost impossible...
الصفحة 640 - Sigillarice, the variations in the leaf-scars in different parts of the trunk, the intercalation of new ridges at the surface representing that of new woody wedges in the axis, the transverse marks left by the stages of upward growth, all indicate that several years must have been required for the growth of stems of moderate size. The enormous roots of these trees, and the condition of the coal-swamps, must have exempted them from the danger of being overthrown by violence.
الصفحة 637 - The laminae of pitch- or cherry-coal, says Dr. Dawson, when carefully traced over the surfaces of accumulation, are found to present the outline of flattened trunks. This is also true to a certain extent of the finer varieties of slate-coal ; but the coarse coal appears to consist of extensive laminae of disintegrated vegetable matter mixed with mud.
الصفحة 640 - ... resolved by decay into shells of bark and loose fragments of rotten wood, which currents must have swept away, but which the most gentle inundations, or even heavy rains, could scatter in layers over the surface, where they gradually became imbedded in a mass of roots, fallen leaves, and herbaceous plants.
الصفحة 66 - They occur generally along the margins of the coal-areas, near their old shores ; and, as might be expected under such circumstances, they are associated with or replaced by beds of conglomerate derived from the neighbouring highlands of Devonian or Silurian rocks. When the conglomerates are absent, alternations of sandstones with sandy and calcareous shales occur, with frequent changes in character of the organic remains. The general aspect being that of muddy estuarine deposits, accumulated very...
الصفحة 496 - Babbage), a process which has long since ceased in the pala;ozoic regions. Both normal metamorphism and volcanic action are generally connected with elevations and foldings of the earth's crust, all of which phenomena we conceive to have a common cause, and to depend upon the accumulation of sediments, and the subsidence consequent thereon, as maintained by Mr. James Hall in his theory of mountains. The mechanical deposits of great thickness...
الصفحة 85 - ... the solid and coarser from the finer and liquid particles, into different zones or layers ; those composed of the former moving less readily than those composed of the latter ; and also that the former will, by the friction attending this process, be turned round so as to bring their major axes into the line of direction of the movements ; and, if susceptible of tension or disintegration, will be elongated or drawn out in the same direction. In illustration of this law, specimens of marbled paper...
الصفحة 495 - Mr. Babbage* has shown that the horizons, or surfaces, of equal temperature in the earth's crust, must rise and fall, as a consequence of the accumulation of sediment in some parts, and its removal from others, producing, thereby, expansion and contraction in the materials of the crust, and thus giving rise to gradual and wide-spread vertical movements. Sir John...
الصفحة 496 - results of the same cause, and depend upon the differences in the chemical composition of the sediments, the temperature, and the depth to which they are buried : while the unstratified nucleus of the earth, which is doubtless anhydrous, and according to the calculations of Messrs.