1897.] NATURAL SCIENCES OF PHILADELPHIA. 429 



" plotik," but rarely on a barren alluvial bed under which is found 

 a second auriferous bed which reposes directly on the " plotik." 



The auriferous placers are found in the valleys of rivers and 

 brooks, or in dry ravines, and, of course, follow the axis of their 

 depressions. A gold nugget weighing 36 kilogr. (lbs. 79.2) was taken 

 from the Tzarewo-Alexandrowsky in the Miass district. Often a 

 slender thread in the placer is found to be richest in gold, and 

 probably indicates the strongest current. The gold of the explored 

 placers varies between 0*57 gram to 2-69 grams per tonne. A larger 

 yield is rare and when found is in the small placers, or in small parts 

 of large placers where it sometimes reaches 16 kilos, per tonne. It 

 is usually accompanied by Magnetite, which is obtained in the wash- 

 ings as sand called " Schlich." More rarely this sand is composed of 

 Hematite, Ilmenite and Chromite. Frequently Quartz and often 

 Platinum, Garnet, sometimes Zircon, Disthene and Diamonds are 

 obtained. The richness of the Oural placers does not seem to depend 

 on that of the neighboring rocks. The most important placers are in 

 regions of greenstones, crystalline, talcose and chloritic schists, etc. 

 Tbe regions of granite, gneiss and mica schist are less productive. The 

 placers on limestones are often found to be peculiarly rich. In this 

 case the rock is cut out in the form of natural buckets, in which the 

 gold is deposited. The Oural placers are post-tertiary, or recent 

 deposits, containing objects fashioned by man, and occasionally post- 

 pliocene deposits containing the remains of mammoths, rhinoceros, 

 etc. Almost all are on the east, very few on the west slope, of 

 the Oural divide. Among the crystalline stratified rocks here are 

 gneiss with Biotite, Muscovite, with two micas, amphibolic, uralitic, 

 etc.; micaceous, talcose, chloritic, siliceous amphibolic schists; 

 various phyllites and quartzites. Among the crystalline schists, 

 limestones and dolomites (marbles) are found sometimes with organic 

 remains. Among the massives, granites, various syenites, miaskite 

 (Nepheline syenite with Biotite), quartz porphyries, felsite, ortho- 

 porphyries, diorite, gabbro, norite, diabase, various porphyrites, 

 various peridotites, diallages and pyroxenites, serpentine and a 

 mixture of Corundum and Anorthite. Many of these have been sub- 

 jected to more or less dynamic metamorphism, to which among 

 other things the green and uralitic schists owe their existence. The 

 mutual relations of the various formations here are confused from 

 the dislocation of all the deposits (with the exception of those of 

 the tertiary, post-tertiary and upper cretaceous, which latter is rarely 



