436 E. T. Hardman— White Chalk of Tyrone. 



was perfectly visible, apparently iu the same quantity as in tlie first 

 specimen. Its presence was then confirmed by other tests. 



Although this of course affords no direct evidence as to the exist- 

 ence of the metal throughout the chalk here, it is curious that it 

 should be detected in samples procured at such a distance from each 

 other if it were not so. 



The idea then arose that it might have been carried down from 

 the basalt in aqueous solution. Accordingly a piece of the basalt 

 which crops out about 160 yards north-east of the Chalk Quarrj^ in 

 Legmurn was procured,^ and examined in the same way as the Chalk 

 had been. In this also zinc was discovered, and in very appreciable 

 amount ; so much so, that I doubt not had I had time to make a 

 quantitative determination, I should have been able to estimate it. 



There can be little doubt, therefore, the zinc that occurs in the 

 Chalk, probably as carbonate, which would be indistinguishable on 

 inspection, has been carried down from the basalt in aqueous solution. 

 In what form it exists there however must be uncertain. 



[It is true that in most mineralogical works there is no direct 

 mention of the occurrence of zinc compounds in igneoi^s or volcanic 

 rocks, ^ but it seems to be implied in one or two instances ; and it 

 certainly appears to be quite possible that many of them would be 

 formed both in the wet and in the igneous way, in such rocks. At 

 first sight it might be surprising that such a volatile metal as zinc 

 would withstand the great heat of molten rock and remain undissi- 

 pated ; yet several zinc minerals have been artificially formed in 

 furnaces, and under other applications of heat. Franklinite, a variety 

 of magnetite containing zinc and manganese, found workable in the 

 metamorphic Silurian limestone of New Jersey, has been imitated by 

 Delesse, by the action of sesquichloride of iron and chloride of zinc 

 on lime, under the influence of heat.^ Zincite or red oxide of zinc 

 has been obtained in the iron furnaces of Silesia and New Jersey, 

 and in zinc furnaces at Siegen.'' Blende has resulted artifically 

 from subjecting heated oxide or silicate of zinc to the vapour of 

 sulphur, and is found in the furnaces at the Freiberg smelting 

 works. ^ " It occurs in both crystalline and sedimentary rocks." 



[Thus it would seem to be very possible for some zinc compounds 

 to have had a contemporaneous origin with the basalt. On the 

 other hand, the zinc may have been introduced at a later period by 

 the agency of water, in the same way that carbonates of lime, 

 magnesia, and iron, have been, and notably the zeolites, which are 



1 The spot from wliieli the basalt was obtained is about 300 yards from the 

 Chalk Quarry. 



~ Mr. Thomas Davies, E.G. 8.., of the Department of Mineralogy in the British 

 Museum, informs me that Professor Scacchi, of Naples, states that Blende (Zn S) 

 occurs occasionally — in association with galena— in the volcanic breccias of Monte 

 Sorama. — Edit. Geol. Mag. 



3 Dana's System of Mineralogy (1868), p. 153. 



* Ibid. p. 1 35. 



' Ibid. p. 50. (Here, too, the removal of the obnoxious zinc from the lead is a 

 most difficult problem. See Percy's Metallurgy of Lead, p. 325.) , 



•^ Ibid. p. 49. 



