METZ, P., u. H. G. F. WINKLER: Geochim. Cosmochim. Acta 27, 431 (1962).  WINKLER, H. G. F.: Die Genese der metamorphen Gesteine. 2. Auf!. Berlin-Heidelberg-New York: Springer 1967.  METZ, P.: Geochim. Cosmochim. Acta 31, 1517 (1967).  GREENWOOD, H. ].: Carnegie Inst. Washington, Year Book 61, 82 (1962). These three equilibrium curves are represented schematically in Fig. 1 according to thermodynamic calculations. From diagram Fig. 1 it is evident that the paragenesis tremolite + calcite + dolomite commonly observed in metamorphosed siliceous dolomites can occur only in the T-Xco.-field above curve (4) and to the right of curve (3). Therefore, in order for this paragenesis to have been formed at a total gas pressure of 1,000 bars, the temperature must have been in excess of 490 ± 10°C and the gas phase must have been rich in CO2 at the time of metamorphism. A detailed description of the formation of talc and tremolite by the metamorphism of siliceous dolomites will be published soon. We thank the Deutschen Forschungsgemeinschaft for financial support and equipment that made this investigation possible.