GEOLOGICAL SOCIETY OF LONDON. 



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ocean. Subsequent periods of disruption are proved by the 

 lines of disturbance in the Permean series on the immedi- 

 ate flank of the Ural Mountains, and connected with dis- 

 locations which have affected them. The patches of Jurassic 

 rocks at the northern and southern extremities of the range 

 are considered by the authors to have been subsequently 

 desiccated, and the absence of strata of that age throughout 

 the great mass of the chain, or for 12° of latitude, to prove 

 that it was constantly above the level of the sea during 

 the Jurassic epoch. Between that period and the accu- 

 mulation of the gold alluvia, there are no signs of any great 

 changes in the physical structure of the Ural, and the only 

 deposits assignable to that interval, are certain trachytic 

 grits and beds of lignite, which, it is conceived, may have 

 been formed in lakes. 



The authors next proceed to describe the gold alluvia 

 distributed along the eastern flank of the chain, and to 

 point out, first, the connexion which subsists between this 

 superficial detritus, and the adjacent rocks, and afterwards 

 to deduce from the evidence afforded by the deposits, the 

 true age of the accumulation. The authors are of opinion 

 that the quartzose and other veins from which the gold 

 detritus was derived, were produced by one of the last of 

 the igneous intrusions which have affected the Ural Moun- 

 tains, as the veins intersect, not only the schists and serpent- 

 ines, but even the granitic and syenitic rocks. They also 

 show that the gold alluvium belongs to the ordinary, coarse, 

 local detritus of the country, and has been derived from 

 the adjacent rocks. With respect to the relative age of the 

 deposit, it is proved that the accumulation must have taken 

 place subsequently to the period when the chain had re- 

 ceived, to a great extent, its present modification of slopes 

 and valleys, yet anterior to the existing conditions of the 

 surface, because it occurs in considerable thickness at points 



