592 PETROLOGICAL ABSTRACTS AND REVIEWS 



cordierite-anthophyllite, quartz-cordierite-, cordierite-, and andalusite- 

 quartz-mica-rocks, cordierite-gneiss, plagioclase-biotite-gneiss, cumming- 

 tonite-amphibolite, and the skarn rocks. A great many chemical 

 analyses are given, and they are recomputed into the norm as well as 

 into Osann's system. Further, all analyzed rocks whose mode could 

 be determined under the microscope have been recomputed into the 

 mode, an example which might well be followed by petrographers in this 

 country. 



Fenner, Clarence N. "The Stability Relations of the Silica 

 Minerals," Amer. Jour Sci., XXXVI (1913), 331-84. 

 The following inversion-points were determined at atmospheric 

 pressure. 



87o°±io° quartz ±5 tridymite 

 i47o°± io° tridymite^cristobalite 



Velocity of transformation very slow. 



a-quartz->/?-quartz 575 



/3-quartz->a-quartz 570 



a-tridymite->/3i-tridymite n 7° 



/?i-tridymite-^/3 2 -tridymite 163 



a-cristobalite ->/?-cristobalite 274 to 220 , depending upon the previous 

 heat treatment. 



/3-cristobalite->a-cristobalite 240 to 198 , depending upon the previous 

 heat treatment. 



The transformation in the last six cases takes place promptly. 

 The melting-point of cristobalite is ca. 1,625°, while quartz is at least 

 1 5 5° lower. 



Fermor, L. Leigh. "Preliminary Note on Garnet as a Geological 



Barometer and on an Infra-Plutonic Zone in the Earth's 



Crust," Records Geol. Surv., India, XLIII (1913), 4 I ~47- 



A comparison of the specific gravities of certain garnet-bearing rocks 



with the specific gravities of the same magmas crystallizing in normal 



minerals showed that the garnet-bearing rocks occupied from 10 to 20 



per cent less room. From this the author concludes that garnet-bearing 



rocks, such as kodurite, eclogite, etc., are high-pressure forms of normal 



rocks. He therefore postulates the existence, below normal plutonic 



rocks, of a shell characterized by garnets wherever a sesqui-oxide radicle 



exists. For this shell he proposes the term "infra-plutonic." Another 



