. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. Fissures left vacant by decomposed trap. Strathaird, Skye. (MacCulloch.) Fig. 679. more tough and hard than the sandstone; but chemical action, and chiefly the oxidation of the iron, has given rise to the more rapid decay. There is yet another case, by no means uncommon in Arran and other parts of Scotland, where the strata in contact with the dike, and for a certain distance from it, have been hardened, so as to resist the action of the weather more than the dike it
. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. Fissures left vacant by decomposed trap. Strathaird, Skye. (MacCulloch.) Fig. 679. more tough and hard than the sandstone; but chemical action, and chiefly the oxidation of the iron, has given rise to the more rapid decay. There is yet another case, by no means uncommon in Arran and other parts of Scotland, where the strata in contact with the dike, and for a certain distance from it, have been hardened, so as to resist the action of the weather more than the dike itself, or the surround- ing rocks. When this happens, two parallel walls of indurated strata are seen protruding above the general level of the country and fol- lowing the course of the dike. As fissures sometimes send off branches, or divide into two or more fissures of equal size, so also we find trap dikes bifurcating and ramifying, and sometimes they are so tortuous as to be called veins, though this is more common in granite than in trap. The accompany- ing sketch (fig. 679) by Dr. MacCulloch represents part of a sea-cliff in Argyle- shire, where an overlying mass of trap, 5, sends out some veins which terminate downwards. Another trap vein, a a, cuts through both the limestone, c, and the trap, b. In fig. 680, a ground plan is given of a ramifying dike of greenstone, which I observed cutting through sandstone on the beach near Kildonan Castle, in Arran. The larger branch varies from 5. Trap veins in Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lyell, Charles, Sir, 1797-1875. New York, D. Appleton and co.
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectgeology, bookyear1868
