Metamorphic Rocks of Bergen ²

Abstract

THE metamorphic rocks of the Bergen Peninsula in Norway continue to attract the attention of Norwegian geologists, and we have before us, as an addition to the well-known works of Naumann, Leopold von Bucb, Esmark, Keilhau, Kjerulf, and Hjörtdal, a new elaborate and interesting work by M. Hans H. Reusch, which deals with the same subject. These rocks consist, as is known, of a variety of quartziferous talc-mica schists, diorite, clay-slates, conglomerates, and strongly-developed gneisses and granites. Various and very different opinions have been expressed as to the origin of these rocks. The researches of M. Reusch give a key to this question, as he has discovered in the clay-slates, which seem to constitute the upper part of these vertical strata, numerous fossils belonging to the lower part of the Upper Silurian formations, namely Halysites catenularia and Cyathophyllum, changed into white calcareous spar, a few tubular bodies (presumably Syringophyllum organum), some gasteropods (Murchisonia or Subulites?) some trilobites, as Calymene, also Phacops or Dalmannites, and some brachiopods. The presence ot these fossils is the more interesting as the whole series of schists was often considered as of igneous origin. As to the gneisses and gneisso-granites of the peninsula, M. Reusch has given great attention to their structure and to the remarkable results of pressure which the rocks have under gone. He shows how granitic veins were folded and crumpled, how a kind of transversal stratification has arisen in beds of stratified gneiss under the influence of pressure, and he con cludes, from an accurate study of the subject, that altogether the rocks show a far greater degree of plasticity than might have been supposed. “It seems that there are masse, as, for in stance, the gneiss of Svenningdal, that have on one side a true stratified structure (not merely parallel or schistose structure) which could hardly be found in a rock of igneous origin, and on the other side send veins, or have included fragments which have undergone metamorphic changes.”