REVIEWS 755 
Considerable space is given to their texture or structure, with special 
reference to their interpretation in terms of the occurrence of the 
rocks and the order of crystallization of the mineral constituents. 
The age of igneous rocks and their alteration and metamorphism are 
briefly treated, and a system of classification is given without discussion 
of the principles on which it is based. ‘The classification followed is 
the same as that employed in Professor Rosenbusch’s work on the 
Microscopical Physiography of the Massive Rocks, with slight modifica- 
tion in the divisions embracing “ 7vefengesteine” and “ Gang gesteine.”’ 
An age distinction has disappeared from the grouping of “Ergussges- 
teine,” so that liparite and quartz-porphyry are described together. 
The description of each class of rocks embraces the mineralogical and 
microscopical characteristics, besides the chemical composition, which 
is shown in ample tables of analyses both of the rocks as a whole 
and of separate mineral constituents. This feature is a very marked 
addition to the treatment of the subject in the Microscopical Physiog- 
raphy of Massive Rocks. ‘The metamorphism of igneous rocks them- 
selves and that produced by them upon adjacent rocks is described in 
immediate connection with the description of the unaltered rocks. 
The part devoted to stratified rocks follows the same general plan 
as Part I. The rocks are classified under the heads of: precipitates, 
psephites and psammites, silica rocks (not previously described), car- 
bonate rocks, iron rocks, clay rocks, porphyroids and fossil fuels. In 
this part also, considerable is introduced that belongs to the subject of 
metamorphism. 
Part III treats of the crystalline schists, their composition, geo- 
logical occurrence, texture and classification. Crystalline schists are 
said to be eruptive or sedimentary rocks that have attained geologi- 
cal transformation chiefly through the codperation of geo-dynamic 
agencies. The classification of these rocks is that commonly used 
and the author recognizes its artificial and unsatisfactory character 
but considers our knowledge and judgment in the matter not yet 
sufficiently advanced to warrant any attempt at its betterment at this 
time. The order followed is: gneisses, mica-schists, talc-schists, 
chlorite-schists, amphibole and pyroxene rocks, serpentine, rocks of 
the lime series, magnesia series, iron series, and emery (corundum). 
In each class the mineral and chemical compositions are described 
together with the texture and the varieties of rock embraced within 
each class. 
