. Elements of geology. Geology. Fig. 94. mica-schist. Fig. 94. repre- Sy enitic greenstone dike of Jsrasodden,Christiania. sentS a grOUnd plan, where the dike appears eight paces in width. In the middle it is highly crystalline and gra- nitiform, of a purplish co- lour, and containing a few crystals of mica, and strong- ly contrasted with the whitish mica-schist, hetween which and the syenitic rock there is usually on each side a dis- tinct black band, 18 inches wide, of dark greenstone. When first seen, these bands have the appearance of two accompanying dikes ; yet they are, in fact, only th
. Elements of geology. Geology. Fig. 94. mica-schist. Fig. 94. repre- Sy enitic greenstone dike of Jsrasodden,Christiania. sentS a grOUnd plan, where the dike appears eight paces in width. In the middle it is highly crystalline and gra- nitiform, of a purplish co- lour, and containing a few crystals of mica, and strong- ly contrasted with the whitish mica-schist, hetween which and the syenitic rock there is usually on each side a dis- tinct black band, 18 inches wide, of dark greenstone. When first seen, these bands have the appearance of two accompanying dikes ; yet they are, in fact, only the different form which the syenitic materials have assumed where near to or in contact with the mica-schist. At one point, a, one of the sahlbands termi- nates for a space; but near this there is a large detached block &, having a gneiss-like structure, consisting of hornblende and felspar, which is included in the midst of the dike. Round this a smaller encircling zone is seen, of dark basalt, or fine-grained greenstone, nearly corresponding to the larger ones which border the dike, but only one inch wide.* The fact above alluded to, of a foreign fragment, such as h (Fig. 94.), included in the midst of thd' trap, as if torn off from some subjacent rock or the walls of a fissure, is by no means uncommon. A fine illus- tration is seen in a dike of greenstone, ten feet wide, in the northern suburbs of Christiania, in Norway, of which the annexed figure is a ground plan. The dike passes through shale, known by its fossils to be- long to the transition, or Silurian series. In the black base of greenstone are angular and roundish pieces of gneiss, some white, others of a light flesh-colour, some without lamination, like granite, others with laminae, which, by their various and often opposite directions., show that they have. Greenstone dike, with fragments of gneiss, Sorgenfri, Christiania. * This dike has been described by Professor Keilhau, of Christiania, in whose company I e
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Keywords: ., bookauthorlyellcharlessir17, bookcentury1800, booksubjectgeology
