B. H. Rastall — The Genesis of Tungsten Ores. 36T 



been bodily iiplifted from far below sea-level to a height of many- 

 hundreds of feet in post-Tertiary times, as attested by the shell 

 beaches that girdle their flanks, and when the present living 

 mollusca were tenanting the present seas that wash their shores? Is 

 it a rational induction or the reverse to argue that if such enormous 

 movements in such tough rocks were the result of lateral thrusts 

 caused by shrinkage of the earth's crust, which both induction and 

 experiment combine to establish, that thrusts on this scale could 

 hardly occur without the most serious breakages and fractures ? 



I have very little doubt, therefore, that the chalk dislocations of 

 the Baltic were consequential on the uplift of the great hog-backed 

 Scandinavian peninsula, and were almost certainly synchronous with 

 the opening of the Baltic breach, which certainly dates from the 

 human period. 



[To he continued.) 



Y. — The Genesis of Tungsten Ores. 



By R. H. Eastall, M.A., F.G.S. 



{Concluded fr 0711 the Jidy Number, p. 296.) 



Part IV : Secondary Tungsten Deposits. 



AT the present time a large proportion of the world's supply of 

 tungsten ores comes from secondary (detrital) deposits of various 

 kinds, formed by the normal denudation and redeposition of primary 

 ores exposed at the surface to the agents of weathering and 

 transport. It is impossible to form any idea of what fraction 

 of the world's output actually comes from these sources, since the 

 published-statistics do not draw any distinctions in this respect, but 

 the amount is undoubtedly large. Although of such great economic 

 value, the secondary deposits do not show any features of special 

 interest, and a lengthy description is unnecessary. 



From this point of view the outstanding feature of the tungsten 

 minerals is their great stability and resistance to any kind of 

 chemical or mechanical alteration. Hence, like cassiterite and gold, 

 they are particularly prone to occur in both residual and alluvial 

 deposits. In many of the published descriptions, and especially in 

 the technical journals, a good deal of confusion is found to exist 

 between the residual deposits, where the material is still more or 

 less in place, and the true alluvial or transported deposits. From 

 their very stable character it follows that tungsten minerals must 

 tend to remain unaltered in the gossan of lodes and other masses and 

 also to concentrate in the shoad. Hence a kind of secondary enrich- 

 ment is found on the weathered outcrops of lodes. This is, of 

 course, not really an enrichment in tungsten ores, but rather 

 a removal of otlier constituents of a less stable nature, leading to 

 a concentration of the more resistant minerals of the weathered mass. 

 From their stability and high density it also follows that the 

 tungsten minerals are specially liable to occur as placers and other 

 forms of transported deposits. The same properties also lead to 

 a natural concentration in such deposits, especially in the lowermost 

 layers, resting on the bed-rock, and in natural riffles. In this 



