PETROLOGICAL ABSTRACTS AND REVIEWS 405 



An entirely distinct type of metamorphism, common along the borders of 

 pegmatite dikes, is conspicuous in the presence of aegirite and riebeckite, as 

 well as of long, needle-like titanite crystals. The latter, as well as the soda- 

 rich pyroxene and amphibole, are attributed to an increase in soda-content, 

 with a corresponding decrease in calcium oxide. The formation of aegirite 

 ana riebeckite takes place especially in the absence of alumina. 



GoLDSCHMiDT, V. M. Geologisch-PetrograpMsche Studien in Hoch- 

 gehirge des Sudlichen Norwegens: III, Die Kalksilikatgneise 

 und Kalksilikatglimmerschiefer des Trondhjem-Gebiets, Christi- 

 ania, 191 5. Pp. 37, pis. (and maps) 2, table i. 

 This is a summary of investigations in the zone of the Gula gneisses and 

 slates of the Trondhjem district, Norway. The Gula group is probably of 

 Silurian age. The rocks are highly metamorphosed,. and the particular facies 

 here studied are those rich in calcium silicates. Several zones of the schists are 

 recognized, varying in their chlorite and biotite content. The results of extreme 

 metamorphism may be summarized as follows: (a) Highly calcareous rocks 

 lose their biotite content, this being replaced by plagioclase, amphibole (or 

 pyroxene), and potash feldspar; or, (b) If poor in calcium oxide, the rocks are 

 converted into a biotite-plagioclase rich slate, with varying amounts of quartz. 

 In the former case the rock texture and constituents vary markedly with varia- 

 tions in degree of metamorphism. The latter type may be readily shown to 

 be of sedimentary origin by means of microscopic study, corroborated by 

 chemical analysis. Methods given in the text for calculating the theoretical 

 constitution of these meta-sedimentaries are most instructive. 



GoLDSCHMEDT, V. M. Geologisch-Petrographische Studien im Hoch- 

 gebirge des Sudlichen Norwegens: IV, Vhersicht der Eruptiv- 

 gesteine im Kaledonischen Gebirge zwischen Stavanger und Trond- 

 hjem. Christiania, 1916. Pp. 140, pis. (and maps) 7, table i, 

 figs. 2. 



Reports the petrologic findings in an area about 600 kilometers long lying 

 between Stavanger and Meraker, in southern Norway. This area bears igne- 

 ous rocks of all sorts, from acid to basic. It is impossible to treat these as 

 though they were all products of a single magmatic province; more probably 

 they belong to three separate groups, as follows: (i) Green lavas, tuffs, and 

 intrusives — the differentiation products being chiefly basic; (2) Anorthosite- 

 charnokite rocks, with numerous differentiation products; and (3) Tonalite- 

 granodiorite magmas, with many differentiation products. Some few of the 

 rocks, indeed, do not even fit into such a classification. 



