178 Reviews — Geology of the N. Urals. 



in the Sierra de Ronda they pass gradually into peridotites with 

 pyroxene. The alluvial deposits also present important differences. 



The memoir concludes with the description of the peridotites of 

 Khrebet-Salatin, in the northern part of the Urals, which differ in 

 their mode of occurrence from those of the classical platiniferous 

 localities and resemble those of the Sierra de Ronda. Platinum has 

 been found i n the alluvia of rivers draining Khrebet-Salatin, but no 

 satisfactory results from the economic point of view have as yet been 

 obtained. 



Although the result of the comparison of the typical platiniferous 

 localities of the Urals with the Sierra de Ronda is not exactly 

 encouraging, it is to be hoped that M. Orueta's interesting discovery 

 will be followed up, and that it will lead to an important addition 

 to the world's supply of platinum. 



IV. — Geology and Petrography of the Urals. Recherches 

 Geologiqtjes et Petrographiques sur l'Oural dtt Nord : LE 

 Bassin des Rivieres Wagran et Kakwa. Par Louis Duparc 

 et Margarite Tikanowitch. Mem. Soc. Phys. Hist. Nat. 

 Geneve; Quatrieme Memoire, pp. 69-168, avec 11 figures et 

 2 planches. 



fllMS memoir consists mainly of detailed petrographical descriptions 

 1_ of rocks collected during explorations made in 1903. The 

 district lies to the east of the main watershed of the Urals and is 

 traversed by lat. 60° N. No detailed map exists, and the country, 

 which is largely covered with forest, is practically uninhabited. 



Passing eastward from the line which separates the rivers of 

 Europe from those of Asia one traverses a zone of quartzose schists 

 and quartzites, the latter forming anticlinals in the former. This is 

 succeeded by a zone of hornblende rocks, more or less schistose, some 

 of which appear to have belonged originally to the diabase family. 

 On the right bank of the Wagran green quartzose schists are followed 

 by plutonic rocks, consisting of gabbro-diorites, quartz-diorites, and 

 granites with plagioclase. Normal fresh gabbros are also present on 

 an extensive scale, but pyroxenites and dunites are comparatively 

 rare, and when they do occur the pyroxenites do not form a zone 

 round the dunites as they do in other parts of the Urals. The dyke 

 rocks include beerbachites with hornblende, diorite-porphyrites, and 

 a peculiar jock, intrusive in dunite, to which the authors apply the 

 name of gladkaite. This is a fine-grained rock composed of apatite, 

 magnetite, biotite, muscovite, hornblende, epidote, quartz, and 

 plagioclase felspars, which vary in composition from labradorite to 

 oligoclase-andesine, andesine being the dominant variety. 



The petrographical descriptions, which make up more than two- 

 thirds of the memoir, are full of details as to the birefringence and 

 other optical characters of the minerals. Numerous chemical analyses 

 are given, but they are not up to the standard of the best modern 

 work, and the name of the analyst is not mentioned. 



