Page:The Journal of geology (IA journalofgeology11893univers).pdf/439

like that pointed out by the present writer in the greenstone-schists and associated rocks of Lake Superior. (Bull. U. S. Geol. Surv., No. 62).

Professor Termier of the Ecole des Mines at Saint-Etienne has given in his essay on the constitution of the Vanois massif in Savoy, another excellent contribution to our knowledge of the effects of orographic movement in metamorphosing Alpine sediments of Carboniferous and Triassic age. This is all the more welcome from France where dynamometamorphism has been rather slow to gain recognition, in spite even of the convicting demonstrations by Gosselet in the Ardennes. The schistes lustrés, which bound the Vanois massiv on the east, considered by Lory as upper Triassic, are made by Termier pre-Carboniferous. The principal horizons which have been studied with reference to metamorphism are the Permian and Trias. The former is represented mainly by quartzites and phyllites, altered and recrystallized in proportion to the disturbance they have suffered. In the phyllites rutile, sphene, tourmaline, garnet, zoisite, epidote, glaucophane, chloritoid, various micas and feldspars, and quartz have been abundantly developed. Many interesting details and figures are given to illustrate the development of these new minerals. Albite crystals by their growth in the phyllite have sometimes displaced all, or only a part of the original schist constituents, while in other cases they have not disturbed their position at all. Various minerals are traced in their gradual development from indistinct nodules to perfect crystals. Only the metamorphism of sedimentary beds is considered, and the general conclusion is reached that their alteration is independent of eruptive action, and entirely conditioned by the heat produced by orographic movements. This heat is supposed to have been very gradually produced and very slowly dissipated. The author thinks that a temperature of 200 to 250 C., continued through ages, would suffice to crystallize new compounds like feldspar, quartz, carbonates, tourmaline, chlorite, micas, ilmenite, rutile, etc., without affecting the bulk composition of the rock. In exceptional cases an intenser movement might give a temperature of 300 C., sufficient to produce amphibole, which will appear as glaucophane, if, as in his Permian beds, the original sediments are very rich in soda.