REVIEWS. 
Le PLATINE ET LES GiTES PLATINIFERES DE L’OURAL ET DU MONDE. 
By Lovuts Duparc and Marcuerite N. TrkonowitcH. Quarto, 
pp. vi-+ 542, with xi plates and atlas. Geneva: 1920. 
per oe DUPARC’S researches in the Urals began in 1900. 
with an examination of the platinum deposits of the Koswinsky 
district, and have been extended until they include the central 
mountain-belt from 534 degrees to 614 degrees latitude. Important 
memoirs on certain districts have already appeared, besides numerous 
smaller contributions, chiefly petrographical, by the Professor and 
his coadjutors in the laboratory at Geneva. The work now before 
us presents in final shape the results of the whole investigation ; 
while its scope has been further extended to include more briefly 
the other platinum-producing countries of the world, besides 
a number of technical matters. 
The Ural chain is folded towards the west, and forms part of the 
Hercynian orographic system, though there is evidence of earlier 
movements on the same lines. In the axis of the chain appear 
crystalline schists, which are invaded by a great profusion of igneous 
rocks, mainly basic and ultrabasic, and it is to these intrusive rocks 
that the geological interest chiefly attaches. Of first importance are 
the dunites, which form oval masses with their long axes parallel 
to the mountain-chain. Each of the several occurrences exhibits 
the same relations, being bordered by a zone of pyroxenites, and 
again by an outer zone of gabbros and allied types. The main body 
so constituted is further traversed by numerous dykes, presenting 
a wide range of variety. Four chapters are devoted to the detailed 
petrography of these rocks; the dunite and allied peridotites ; the 
pyroxenites and koswites, a group of rocks composed of olivine, 
augite, hornblende, chrome-spinel, and interstitial magnetite; the 
gabbros and their allies, including the tilaites, in which pyroxene 1s 
strongly preponderant over felspar, and often imparts a pseudo- 
porphyritic character; and finally the dyke-rocks, which embrace 
a great variety of types. Since many of these rocks have already 
been described, they do not call for particular notice here; but we 
may mention in passing the “‘ plagiaplites ’’ with primary brecciation, 
which afford strong ground for the belief that the uralitization of 
pyroxenes may be a magmatic process. 
It has long been established on circumstantial evidence that the 
platinum found as grains in river-gravels and sands is derived from 
ultrabasic plutonic rocks; but so sparsely is it distributed in its 
primary situation, that only by prolonged search has such occurrence 
been verified. Our authors are able to prove directly that platinum 
is a normal constituent in very small amount of the dunites and 
pyroxenites of the Urals. In the former it is found either as small 
