REVIEWS 
Die kristallinen Schiefer. By Dr. U. GRUBENMANN. Vol. I, 1904; 
/ Vol. 1907. Zurich. 
The recent work of Dr. Grubenmann, Die kristallinen Schiefer, Vol. I, 
aims, as its author states in the preface, to explain the characteristics of the 
crystalline schists, and their occurrence in the crust of the earth, according 
to chemical-physical laws. Although restricted to one phase of metamor- 
phism, the motive of the work has much in common with The Principles of 
Metamor phism by Dr. C. R. Van Hise. Its general conclusions are, how- 
ever, quite different. 
Dr. Grubenmann briefly follows the historical evolution of conceptions 
relating to the origin of the crystalline schists, and discusses the original 
materials of the schists, and their specific characteristics. The cited criteria 
of sedimentary origin are: stratification, fossil record, micro- and mega- 
fragmental relicts, conglomerates, ripple-marks, delta formations, grada- 
tion phases, chemical composition, and abrupt changes in mineralogical 
composition within very narrow limits. The criteria given for igneous 
origin are: chemical composition, gradation phases, and the preservation 
of original forms of occurrence such as dikes, sills, stocks, and laccoliths. 
The processes enumerated by which the original materials are meta- 
morphosed into crystalline schists are mechanical reconstruction, recrys- 
tallization, and remineralization. ‘The factors which, in conjunction with 
time, enter into these processes are solvents, heat, pressure, and the specific 
characteristics of the original materials. 
Dr. Grubenmann makes a threefold division of the crust of the earth 
into an upper, middle, and lower zone, based on the predominance of one 
or more of the factors of metamorphism. The belt of weathering (Van 
Hise) is excluded from the upper zone. 
The conditions named for the upper zone are moderate temperature 
and low hydrostatic pressure, positive heat-toning,t and powerful stress. 
The predominant pressure effect is mechanical. Heat liberation and 
decrease of volume result from the chemical reactions. The abundance of 
water favors the development of hydroxide minerals, such as sericite, 
t The ‘‘heat-toning”’ of a reaction is positive when the sum of the resulting heats 
of formation exceeds the sum of the heats of formation of the vanished molecule. 
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