760 REVIEWS 
narrative of travel, for the author has described the mining conditions and 
mining processes with an ability that few can equal. The book is well 
illustrated and a very welcome addition to the literature on Alaska. 
W. W. A. 
Schistosity by Crystallization. By FRED. EUGENE WRIGHT. Am. 
Jour. Sci., Vol. XXII, September, 1906. 
The schistose and gneissose textures of many metamorphic rocks have 
been ascribed to the orienting influence of pressures with a stress difference 
acting during the recrystallization of the rock in its new environment— 
solution taking place along the line of greatest strain and deposition along 
the line of least resistance and normal to the maximum stress. In such 
cases the rock cleavage is due to the parallel arrangement of its mineral 
components in planes perpendicular to the line of greatest stress. 
Conditions of experiment in which crystallization under unequal strains 
could take place were effected by using cubes of glasses made by chilling 
melts of different minerals rapidly, and by heating these to the point 
at which crystallization first began, the viscous glass at that temperature 
being still in a state of fair rigidity, and capable of supporting a certain 
amount of unequal strain. ‘Textures similar to those of certain metamorphic 
rocks were produced in this way, and an experimental confirmation of the 
theoretical deductions thus obtained. 
Quartz as a Geological Thermometer. By FRED. EUGENE WRIGHT 
AND EspER S. LARSEN. Am. Jour. Sci., Fourth Series, Vol. 
DOV, pa 162: 
This paper, which is a review and discussion of experiments made by 
the writers in the Geophysical Laboratory of the Carnegie Institution at 
Washington, is an important contribution to the knowledge of mineral 
genesis. By means of the electric resistance microscope the birefringence 
and circular polarization of quartz plates at various temperatures were 
measured and the inversion point (575°) was accurately determined. 
The birefringence of the quartz plates decreases gradually from o° to 
575°, at which point the decrease is very rapid. Beyond this point the 
birefringence increases slightly. The inversion was observed both on 
heating and cooling and the changes are constant and sharply marked. 
There is also a marked change in the angle of circular polarization at the 
inversion temperatures and abrupt change in the coefficient of expansion 
