858 THE JOURNAL OF GEOLOGY. 
others to the works of foreigners add greatly to the usefulness of the 
book for more advanced students. 
The sedimentary rocks are divided into arenaceous, argillaceous, 
calcareous and pyroclastic kinds. Under the first division the general 
terms are defined, and the characters of the derived grains and of the 
authigenous constituents are discussed separately. In this way the 
general characteristics of all arenaceous rocks are given rather than 
the specific character of any one kind of rock. 
In the chapter on argillaceous rocks the general definitions are 
first given, then the characters of the constituent minerals, followed by 
that of the structure. The description of illustrative occurrences 
serves to supply the need of some definite picture of different kinds of 
these rocks. The treatment of calcareous rocks is admirable for so con- 
densed a statement. It deals first with the source and composition of 
these rocks, then the structure of organic fragments; followed by 
oolitic structure, the character of the matrix, and of deep-sea calcare- 
ous deposits. Finally metasomatic changes are described, and British 
examples cited. References to the literature of the subject are num- 
erous and valuable. Pyroclastic rocks are briefly treated. Deposits 
due to chemical or to organic agencies are described in a few short 
paragraphs. 
Under the head of metamorphism the author discusses the general 
principles of the subject, and then describes the changes produced by 
thermal metamorphism upon the different kinds of sedimentary rocks, 
and upon igneous rocks and the crystalline schists. This is followed 
by an account of the effects of dynamic metamorphism upon the min- 
erals and structures of rocks. Very little space is devoted to the petro- 
graphical description of the various kinds of crystalline schists, which 
are grouped under the heads of crystalline schists, gneiss, granulites 
and eclogites. The basis of classification is structure. 
' The book shows careful preparation, and although the reviewer has 
taken exception to some features of it, he would recommend it to all 
those beginning the study of petrology. aren fe 
Boletin de la Comision Geolébgica de México, No. 1 ; Fauna fossil de 
la Sierra de Catorce, San Luis Potosi. By ANTONIO DEL Cas- 
TILLO and Jose G. AGUILERA; pp. 1x +53, with twenty- 
four plates, Mexico, 1895. 
The authors state that they propose in this work to confirm the 
existence of the Jurassic system in Mexico, describing the most 
