PETROLOGICAL ABSTRACTS AND REVIEWS 85 
analyses, but the authors themselves say the computations represent 
“‘as nearly as possible the actual mineral composition of the rocks.”’ 
Changing the granite (granodiorite) and basalt (diorite) analyses would 
probably give a different result for the average sediment, the proportions 
now found being 65 granite to 35 basalt. 
Under the term anamorphism are included cementation, metaso- 
matic replacement, rock-flowage, contact and thermal metamorphism, 
and the constructive changes which tend to make rocks coherent and 
crystalline. The anamorphism of clays through shale, slate, and schist 
to the contact phase, and of sands to sandstones and quartzites, and 
limestones to marble are all shown by numerous straight-line diagrams. 
Dolomitization is briefly touched upon. 
In the fourth chapter of Part II, the dynamic and contact meta- 
morphism of igneous rocks (rock-flowage) is treated. Changes produced 
in katamorphosed products of igneous rocks are clearly anamorphic, but 
igneous rocks do not necessarily pass through a katamorphosed state 
before becoming schists and gneisses. In such cases the katamorphic 
agents must in some way be simultaneously introduced. Alteration by 
hot water in the deeper zones is essentially anamorphic. 
In the chapter on the textures and structures of dynamic metamor- 
phism, rock-cleavage is regarded as the result of the orientation of 
mineral-grains or of the parallel arrangement of mineral-cleavages. The 
orientation of the mineral-grains is ascribed by the writers to differen- 
tial pressures which caused the rock to flow. Recrystallization and the 
development of new minerals at right angles to the pressure and granu- 
lation and rotation of original minerals from random positions are also 
contributing factors in producing schistosity. 
Secondary porphyritic textures, as shown by garnets, staurolite, 
andalusite, etc., are thought to have been caused by recrystallization, 
which took place after rock-flowage had ceased but while the rock was 
probably still under high pressures and temperature. The development 
of gneissic textures is considered, and Becke’s and Grubenmann’s 
views on the conditions of development of the crystalline schists are 
presented. 
Part III treats of the determination of the origin of the metamorphic 
rocks. The first two parts of the book were devoted to the changes pro- 
duced by metamorphism in sedimentary and igneous rocks. In this 
part the field and laboratory methods used in determining the origin of 
these rocks are discussed. Only four pages are devoted to the criteria 
of origin of sediments and residual rocks; a thorough treatment of this 
