Geology and Mineralogy. 



515 



terrestrial life probably reached as far back beyond the oldest 

 known land flora of the Devonian as the interval that has since 

 elapsed and there wonld have been ample time to have developed 

 the anatomical features of Ehynia by reduction, as seems to have 

 been the actual case in the Psilotales. Serious doubts as to the 

 primitiveness of these types arise when the Cordaitalean woods of 

 the Devonian, which are ignored by Arber, are considered. The 

 Archffiopteris flora is regarded by Arber as truly pteridophytic 

 and ancestral to that of the Lower Carboniferous. 



Morphologists will be interested in the unfinished outline of 

 the evolution of the stele sketched in Chapter 7, the stages of 

 which are set forth as — first, a single protoxylem group formed 

 by the simultaneous modification of a set of procambial elements, 

 which took place independently in the main axis and branches : 

 second, the substitution of continuous for purely initial trans- 

 formation, resulting in protoxylem and xylem : third, the forma- 

 tion of a secondary cambium and secondary wood. e. w^ b. 



4. Le Platine et les Gites plaUniferes de VOurcd et du Monde; 

 Louis Duparo and Marguerite-N. Tikonowitch. Quarto. 542 

 pp., 96 figs., 11 pis. and an atlas with 5 maps and 8 pis. 1920. — 

 Professor Duparc with various assistants has been studying the 

 platinum deposits of the Ural Mts. and elsewhere for the past 

 twenty years. The partial results of these researches have been 

 published from time to time in various papers and books. In the 

 present work all this material has been gathered together in an 

 exhaustive monograph. 



The study of the geology of the platinum districts shows that 

 the mother-rock of the platinum is primarily dunite and to a 

 much less extent pyroxenite. In the Ural Mts. the platinum-bear- 

 ing rocks have segregated from the original magma in such a 

 way that the center of the mass is now a dunite which is sur- 

 rounded by a belt of pyroxenite and the whole enclosed hy exten- 

 sive areas of gabbro. The latter rock is practically free from 

 platinum, however. While the book is chiefly concerned with the 

 deposits of the Ural region a chapter is devoted to platinum 

 occurrences elsewhere. The book includes also chapters on the 

 mining methods, metallurgy and uses of the metal. w. e. f. 



5. Elemente der pliysil^cdisclien und cJiemischen KrystaUogra- 

 phie; by Paul Groth. Pp. 363, 4 pis., 962 figs, in text and 25 

 stereoscopic charts. Berlin, 1920. — This is a book which treats 

 the various phases of the subject from the standpoint of the chem- 

 ist. In the chapter on crystals, for instance, the illustrations are 

 all taken from the products of the chemical laboratory. The 

 book is profusely illustrated, for the most part by small but well 

 reproduced figures. The book would have been considered a 

 notable achievement if published under normal conditions and 

 under the present circumstnaces it becomes doubly remarkable. 



w\ E. F. 



6. Crystallography. A Series of Nets for the construction of 



