. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. ^^Vbs&Ou^ ^glWN^S3 Basaltic pillars of the Kiisegrotte, Bertrich-Baden, halfway between Treves and Coblentz. ^Height of grotto, from 7 to 8 feet. rocks the globular structure is so couspicuous that the rock has the appearance of a heap of large cannon balls. According to the theory of M. Delesse, the centre of each spheroid has been a centre of crys- tallization, around which the different minerals of the rock arranged themselves symmetrically during the process
. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. ^^Vbs&Ou^ ^glWN^S3 Basaltic pillars of the Kiisegrotte, Bertrich-Baden, halfway between Treves and Coblentz. ^Height of grotto, from 7 to 8 feet. rocks the globular structure is so couspicuous that the rock has the appearance of a heap of large cannon balls. According to the theory of M. Delesse, the centre of each spheroid has been a centre of crys- tallization, around which the different minerals of the rock arranged themselves symmetrically during the process of cooling. But it was also, he says, a centre of contraction, produced by the same cooling. The globular form, therefore, of such spheroids*is the combined result of crystallization and contraction.* A striking example of this structure occurs in a resinous trachyte or pitch- stone-porphyry in one of the Ponza islands, which rise .from the Mediter- ranean, off the coast of Terracina and Gaeta. The globes vary from a few inches to three feet in diameter, and are of an ellipsoidal form (see fig. 691). The whole rock is in a state of decomposition, " and when the balls," says Mr. Scrope, " have been exposed a short time to the weather, they scale off at a touch into numerous concentric coats, like those of a bulbous root, inclosing a compact nu- cleus. The laminee of this nucleus have not been so much loosened by decompo- sition ; but the application of a ruder blow will produce a still further exfolia- ; f. 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
