Geology and Mineralogy. 73 



10. JElemente der Gestei?islehre, von H. Rosenbusch. 8vo, pp. 

 546. Stuttgart, 1898. — This book is based, as the preface states, 

 on the lectures of the author at Heidelberg. While it claims to 

 be only an elementary treatise, it is much more than that, and will 

 be read with interest by every petrologist as giving the latest 

 views of its author and an excellent resume of the present state of 

 'the science from a certain, rather subjective, standpoint. 



After an introductory chapter on the general principles of 

 petrography and the composition, structure and classification of 

 rocks, the author describes not only the igneous rocks, to which 

 his previous volumes have been devoted, but also the sedimentary 

 rocks and crystalline schists. 



In the portion devoted to the igneous rocks, the essexites, 

 shonkinites and missourites have been raised to the rank of groups 

 of the same order as the granites. The monzonites, for which 

 Brogger has proposed a similar position, are left as a^subdivision 

 of the syenites, while among the effusive rocks a group of trachy- 

 dolerites has been formed. These, according to Rosenbusch, are 

 homologous with the essexites, but, though they resemble these 

 in being intermediate, the examples and analyses which are given 

 resemble more closely Brogger's monzonites. The necessity for 

 the recognition of such groups of intermediate rocks is urgent, 

 but this group, as here given, is the least satisfactory of all, 

 embracing as it does many types which differ much among them- 

 selves, and it seems probable that it will undergo many changes 

 and subdivisions in the future. It may be suggested that the 

 name latite previously proposed by Ransome seems preferable to 

 the coextensive term of trachydolerite used by Rosenbusch. 



The sedimentaries are very fully and satisfactorily treated and 

 the same is true of the metamorphic schists. For schists derived 

 from igneous rocks the author proposes the use of the prefix ortho, 

 and for those derived from sedimentaries the prefix para, so that 

 we would have orthogneiss, paragneiss, etc. 



In general the views held by the author are the same as those 

 •expressed in his previous works. The age distinction is practi- 

 cally banished, but traces of it still survive among the effusivcs. 



The chemical characters of the various rocks are discussed in 

 considerable detail, and a valuable feature is the insertion of 

 tables of typical analyses, not only of the rocks themselves but of 

 their component minerals, many of which are published here for 

 the first time. They are in general well selected, but the almost 

 total lack of references throughout the book, especially for the 

 analyses, is to be deplored, even though such omissions are due 

 to the elementary character of the work. 



But such criticisms are chiefly matters of personal opinion, and 

 the name of the author is sufficient guarantee for the high char- 

 acter of the volume. It should prove a valuable text-book for 

 the German-reading student, and will be a much used addition to 

 the library of every petrologist. h. s. w. 



