THE ORIGIN OF THE WOLFRAM AND CASSITETITTE ORES. 337 



Those writers, in an earlier paper than one quoted below, extended 

 the term to include the formation of pegmatites containing: tourmaline 

 and titanite associated with sulphide ores, regardless of whether 

 such minerals were of destructive or constructive origin. In so 

 (loin* thev believed thev were following competent and predominant, 

 even" if not unanimous, opinion. Thev now agree that the word 

 pneumatolvtic is not wholly satisfactory, if used in its broader sense, 

 as it does not apply with adequate specificness and exclusiveness 

 to a group of post-magmatic sulphides in the case which thev are 

 discussing, nor does it sufficiently imply the close affiliations to the 

 truly magmatio stage exhibited by the group as a whole: while 

 if the term be limited to the narrower sense it is even less satisfactory. 

 To overcome the difficulty, thev have come to the conclusion that 

 there is need for two specific definite names, each independent of 

 the word " magmatio," and thev have coined the words " ortho- 

 tectic " and « pneumotectic " for the purpose. The first designates 

 " those processes and products, strictly magmatio in the narrowest 

 sense, exemplified in the normal crystallization of normal igneous 

 rocks." The second is used for " those next-subsequent processes 

 and products of magma consolidation in which fundamental influences 

 of a. sort that was magmatio in the strictest sense were recognisably 

 modified and to some extent controlled by gaseous constituents or 

 so-called mineralizers which accumulated in relative concentration, 

 by elimination, when in the preceding, orthotectic stage the major 

 portion of the magma crvstallized without incorporating more than a 

 minor portion of those volatile substances that had been components 

 of the initial molten solution. Thus the orthotectic products do not 

 necessarily fail to include metalliferous ores, provided the ore minerals 

 are on an identical footing with the customary rock minerals. But 

 in case it is necessary to assume that the fluidity of the ore minerals 

 requisite for their localization is dependent on the influence of 

 mineralizers, such deposits would fall in the pneumotectic group. 

 Tn consequence of the establishment of these two prior periods it is 

 suggested that the term pneumatolvtic. might be limited to those 

 processes and products in which the fundamentally dominating 

 influence is no longer the straight melt, but is, instead, the still 

 further concentrated and controlling gases. The stages might go on 

 with pneumato-hvdatogenetic if an intermediate term is considered 

 necessary to the hvdrothermal, and beyond, if required or justifiable. 

 Any or all of these periods or divisions would be collectively 



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