R. H. Rastall — The Genesis of Tungsten Ores. 293 



\_Postscript. — The Australian leaf-clus-ters figured by Mr. Etheridge 

 bear a very close resemblance to an Indian specimen reproduced in 

 vol. iii (p. 242, fig. 472) of my Fossil Plants, which shows leaves 

 attached in a close spiral to a supporting axis. 



The late Miss Ruth Holden detected certain differences similar to 

 those pointed out by Professor Zeiller in the stomatal arrangement 

 on Noeggerathiopsis leaves from India as compared vrith that on 

 English leaves of Cordaites, but the results were not published 

 {Fossil Plants, vol. iv, pp. 243-4). Mr. Salini, of Emmanuel College, 

 Cambridge, who has made a further examination of cuticular 

 preparations, liopes in the near future to make a contribution to 

 this subject. — A. C. Seward.] 



II. — The Genesis of Tungsten Ores. 

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



{Continued from the June Number, p. 246.) 



Part III : Scheelite Deposits, 



1,"^R0M the descriptions already given, and from a general survey of 

 ^ the literature of the subject, it is apparent that scheelite is 

 a frequent associate of wolframite in the lodes of magraatic origin. 

 In fact, a certain number of the occurrences already cited, especially in 

 the second part of this paper, might almost as well have been described 

 as scheelite deposits, since the two minerals are found in something 

 like equal quantities. This applies, for example, to a large number 

 of the American and Canadian occurrences, to those of the Malay 

 States, and others. This is only to be expected from general 

 considerations, since gases or solutions containing chemically active 

 tungsten compounds coming in contact vpith calcareous material 

 would naturally tend to form calcium tungstate. The same applies 

 to lead-bearing minerals; hence in a few instances lead tungstate, 

 stolzite, has been found in association "with, scheelite. It is of 

 interest to note that scheelite often contains from 1 to 3 per cent of 

 molybdenum. Wolframite and scheelite are often found in lodes and 

 other masses very closely intergrown, and in many cases there is 

 evidence of much, pseudomorphism. In some cases scheelite has 

 clearly replaced wolframite, while in other cases the reverse holds. 

 The law governing the paramorphism of these minerals is somewhat 

 obscure, and it is not easy to say anything definite on the subject. 

 In this direction further investigation is required, although the point 

 is not perhaps of much practical importance. 



With regard to the predominance of wolframite or scheelite in any 

 particular district, the general rule seems to be that wherever the 

 country rock is more or less calcareous scheelite tends to form ; that 

 this would naturally be so is of course obvious, and the subject 

 hardly seems to need much further elaboration. The general aspect 

 of the problem can be more satisfactorily discussed after consideration 

 of certain deposits in which scheelite is the dominant or even the 

 only tungsten ore present, since such do occur in various parts of the 

 world. 



