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Updated: May 17, 2025
We may sometimes discover the relative age of two trap-rocks, or of an aqueous deposit and the trap on which it rests, by finding fragments of one included in the other in cases such as those before alluded to, where the evidence of superposition alone would be insufficient.
The arrangement by which such a height could be most easily reached would be the superposition of square masses one upon another, each mass being centrally placed on the upper surface of the one below it. The weight would be more equally divided and the risks of settlement more slight than in any other system. Of this type M. Chipiez has restored two varieties.
Now and then a tremendous flash of lightning of a red copper colour broke out behind the obscure superposition of the horizon and the zenith; that sudden release of vermilion flame revealed the horror of the clouds; that abrupt conflagration of the depths, to which for an instant the first tiers of clouds and the distant boundaries of the celestial chaos seemed to adhere, placed the abyss in perspective.
I believe the surest means by which geologic descriptions may be made to survive the change which the science undergoes in proportion to its progress, will be to substitute provisionally in the description of formations, for the systematic names of red sandstone, variegated sandstone, zechstein and Jura limestone, names derived from American localities, as sandstone of the Llanos, limestone of Cumanacoa and Caripe, and to separate the enumeration of facts relative to the superposition of soils, from the discussion on the analogy of those soils with those of the Old World.*
Why ancient and modern Rocks can not be identical. Tests by Superposition and intrusion. Test by Alteration of Rocks in Contact. Test by Organic Remains. Test of Age by Mineral Character. Test by Included Fragments. Recent and Post-pliocene volcanic Rocks. Vesuvius, Auvergne, Puy de Come, and Puy de Pariou. Newer Pliocene volcanic Rocks. Cyclopean Isles, Etna, Dikes of Palagonia, Madeira.
When we reflect on the immense progress made within twenty-five years in the knowledge of the superposition of rocks, it will not appear surprising that my present opinion on the relative age of the formations of Equinoctial America is not identically the same with what I advanced in 1800.
If the regular sequence of the three deposits of pebbles, mud, and stalagmite was the result of the causes above explained, the order of superposition would be constant, yet we could not be sure that the gravel in one passage might not sometimes be coeval with the bone-earth or stalagmite in another.
The uniformities, on the other hand, in the order of superposition of strata on the earth, are empirical laws of a much weaker kind, since they not only are not laws of causation, but there is no reason to believe that they depend on any common cause; all appearances are in favor of their depending on the particular collocation of natural agents which at some time or other existed on our globe, and from which no inference can be drawn as to the collocation which exists or has existed in any other portion of the universe.
The RELIEF of a country cannot be precisely explained on a map, nor can the most erroneous opinions on the locality and superposition of the strata be avoided, if we do not apprehend with clearness the relation of the directing lines just mentioned. Thence it results that the same formations do not constitute the region of plains and that of mountains.
He also says that he "strongly protests against the too frequent use of clay or plaster models, because they are often worse than useless, and not infrequently absolutely immoral in their tendency, because they absorb time and money, which ought more legitimately to be spent on the carving itself." Intelligible Background Outline Better than Confused Foreshortening Superposition of Masses.
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