Geology and Mineralogy. 153 



Becke's point that the thin sections generally used in micro- 

 scopical work are so thin that most interference figures do not 

 show isochromatic curves and that therefore the isogyres are the 

 characteristic phenomena is given proper emphasis. The inter- 

 ference figures shown in most manuals are such as we never see- 

 in everyday work. On the whole, the treatment of interference 

 figures is inadequate, as it is in all manuals. The only adequate 

 presentation of this difficult subject is Becke's masterly exposi- 

 tion, which should be consulted in the original. 1 Probably the 

 second installment, which will deal with practical applications, 

 will remedy this inadequacy. 



The treatment of dispersion has been improved and clarified 

 and is illustrated by excellent figures. The new account of pleo- 

 chroic halos shows more clearly than any other revision in the 

 book one of the notable lines of progress since the fourth edition. 

 The description of the various. kinds of luminescence is new and 

 has been introduced in the hope that it is anticipatory of future 

 advances. 



The descriptions of the various prisms for obtaining polarized 

 light, occupying pages 222-239, seem unnecessarily detailed, in 

 view of the professed purpose of the book ; and they might well 

 be condensed or omitted. The installment ends with the section 

 on the preparation of monochromatic light. 



In conclusion, we can say that the thoroughness of the revision 

 and the care shown in the first installment of the new edition to 

 bring the subject abreast of the times leads us to look forward 

 with anticipation to the succeeding installments of the great 

 source book in microscopic petrography. adolph knopf. 



7. Morphogenese der Oetscherlandschaft. Vienna, 1921, 

 Karl Diwald (published by the Author). Large 8vo, 404 pages 

 with a large folded map, 1 :25,000, and a 21-page supplement 

 containing 70 block diagrams. — This volume is a serious but seem- 

 ingly venturesome effort to interpret the complicated forms of 

 the Oetscher district, near the northern margin of the Alps, about 

 80 kil. west-southwest of Vienna, in terms of successive episodes 

 of erosion prompted by many partial uplifts of the region. 

 Twelve systems of forms are thought to be identified. The book 

 is difficult reading because the text is a veritable ticket of details, 

 without summaries. w. m. d. 



8. New Meteorites; by George P. Merrill (communicated) . — 

 The National Museum reports the receipt of a fragment of a 

 heretofore unknown meteorite (pallasite of the Rockiky type) 

 from Cold Bay, western Alaska. The entire mass as found was 

 in form of a badly oxidized mass of but a few pounds weight, 

 which was at once broken up and in large part lost. The find is 

 of interest, being the second from Alaska proper, the first being 

 that of Chilkat (an iron). Two finds, Skookum Gulch and Gay 



1 Becke, F., Tschermak's Min. Petr. Mitt., vol. 24, pp. 1-34, 1905. 



