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certain truncated anticlines, and infers their order of superposition, the 
reader finds, as a whole, that the field evidence on which his threefold classi- 
fication is based does not stand out very clearly. In fact, the reader gathers 
the impression that the threefold classification is based rather on inferences 
drawn from certain mineral associations than on decisive field observation 
of the existence of three zones. 
Dr. Grubenmann infers that the reactions in the two uppermost zones 
occur with volume-decrease, since the characteristic minerals of this zone 
mostly belong to Léwinson-Lessing’s ‘‘minus” group; i. e., their molecular 
volume is less than the molecular volume of the oxides which compose 
them. Most of his readers will probably not agree to this method, but will 
consider the actual volume-changes involved in the mineral alterations: 
Various investigators have shown that the alterations described as peculiar 
to these zones—chlorization, serpentinization, and sericitization—generally 
involve increase of volume. } 
In the lower zone also he considers the molecular volume relations 
between the minerals and their constituent oxides as indicative of the 
volume-changes caused by the reactions. He argues that the occurrence of 
“plus” minerals, like orthoclase, plagioclase, and sillimanite, indicates 
volume-increase. However, calculations of the actual mineral volume- 
change involved in their formations from other minerals show a decrease in 
volume. 
In the second volume Dr. Grubenmann distinguishes twelve groups on 
the basis of chemical composition, which are delimited by empirically 
derived chemical values. The groups take their nomenclature from the 
rock formations which are peculiar to them. They are: (I) orthoclase 
gneisses, (II) alumino-silicate gneisses, (III) plagioclase gneisses, (IV) 
eklogite and amphibolite, (V) magnesian-silicate gneisses, (VI) jadeite 
rocks, (VII) chloromeianite rocks, (VIII) quartzitic rocks, (IX) lime- 
silicate rocks, (X) marbles, (XI) iron-oxide rocks, and (XII) alumino- 
oxide rocks. Each group is subdivided into orders, which are based on 
the physical characteristics assumed by a group in the upper, middle, and 
lower zone respectively. A group-name takes the prefix ‘‘kata”’ when it 
designates a rock of the first order or of the lowest zone. The prefix 
‘‘meso”’ is applied to rocks of the middle zone or the second order; and 
the rocks of the third order or the upper zone take the prefix ‘‘epi.” Fre- 
quently the orders are subdivided into families, based on mineral compo- 
sition. 
The first step in identifying the position of a crystalline schist in Dr- 
Grubenmann’s system is to ascertain its chemical composition. The per- 
