1894.] Recent Literature. 151 
well as in Europe. The faults of the book are such only when it is 
criticized as a Lehrbuch. Asa manual it is very satisfactory, though 
one would wish that the author had made his list of rock-forming 
minerals more complete than it is, and had given more detailed instruc- 
tions as to the manipulations in some of the investigation methods 
mentioned. Upon comparison with Rosenbucsh’s first volume it is 
found that this treats of forty-four more minerals than does Zirkel’s 
book, but then the Heidelberg volume deals only with microscopical 
petrography. Further, the absence of illustrations from the Lehrbuch 
will prevent its use as a text book for students, and the failure to 
attempt an explanation of the action of mineral plates toward polar- 
ized light will in large measure keep it from even our universities and 
technical schools. But these faults, we repeat, are faults in a text book. 
They are not altogether weaknesses in a hand-book. Zirkel will be- 
come the reference book of petrographers, while Rosenbuesh will 
remain their text book. 
In that portion of the volume occupied with the special discussion 
of massive rocks, the author outlines his classification and gives his 
reasons for it. He declines to recognize the dyke rocks as a well 
established class, and so makes his division (according to structure and 
mineralogical composition) into granular and porphyritic groups, and 
then into types. In the first group, age distributions are disregarded. 
In the second group the old distinction between pre-tertiary and ter- 
tiary volcanics is revived. Petrography is regarded as primarily as a 
study of rock bodies, and secondarily as a branch of geology. 
The lack of illustrations which has already been noted will. not 
detract seriously from the value of the volume as a reference book, as 
the author has no new structures to define and no new rock-types to 
establish. - He gives an excellent resumé of petrographical literature 
and there stops. He has no theories to advance and no attacks to 
his brother investigators, except now and then, a mild one upon Rosen- 
busch, and his discussions upon the literature are uncolored by his 
own views. Now and then a criticism is interjected into the discus- 
sion, but upon the whole the author allows the conclusions reached in 
the articles cited tostand unchallenged, or if they are challenged it is 
by the citation of other authors. In brief the Lehrbuch is an excellent 
résumé of our present knowledge of rocks and a fine reference book 
to petrographical literature. Naturally more interest will be felt in 
the two volumes to appear, than in the first volume, for at least one of 
these will afford a starting point for a systematic petrographical study 
of the crystalline schists. ` - W. 5. B. 
