Norsk Geologisk Tidsskrift, Volum 6Universitetsforlaget, 1922 |
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Passatges populars
Pàgina 146 - A mineral facies comprises all the rocks that have originated under temperature and pressure conditions so similar that a definite chemical composition has resulted in the same set of minerals, quite regardless of their mode of crystallization, whether from magma or aqueous solution or gas, and whether by direct crystallization from solution (primary crystallization) or by gradual change of earlier minerals (metamorphic recrystallization).
Pàgina 145 - The writer proposed to use the term metamorphic facies to designate a group of rocks characterized by a definite set of minerals which, under the conditions obtaining during their formation, were
Pàgina 149 - It has been tacitly assumed that the pyroxenes by metamorphism most likely would be converted into amphiboles. From the view of the facies-conception this statement must be much restricted, and we may say, that uralitization takes place when
Pàgina 149 - excess of magnesia, and in the case supposed the alteration had gone so far as possible at the composition given, and the rock had arrived at an equilibrium.
Pàgina 149 - the diopside may be a stable constituent, viz. in those rocks in which femic lime is present in excess over the hornblende ratio (in
Pàgina 149 - hornblende, and yet the diopside is not an unstable mineral. It is only unstable in the presence of excess of magnesia,
Pàgina 188 - not considered, to a continuous shell round the earth, the whole of which shell is a potential magma. This shell, being composed of rocks of the consistency of a plastic solid, may afford a cushion upon which the isostatic operations of the earth, believed in by some geologists, have their foundation. Any portion of this shell may become a reservoir
Pàgina 144 - from two funds for the advancement of scientific research in my native country, Finland, namely, ALFRED KORDELIN'S General Trust for the Advancement of Progress and Knowledge, and HERMAN ROSENBERG'S Travelling Bursaries Trust of the University of Helsingfors.
Pàgina 31 - entweder auf den Alaunschiefern oder auf dem Birikalk-' liegt, so ist schon dadurch eine Altersbeziehung zum Silur gegeben und ich bin geneigt in ihm, wenn auch nicht gerade einen Vertreter des
Pàgina 138 - GARWOOD. EJ On the important part played by Calcareous Algae at certain geolog, horizons, with