FULGURITES, OR LIGHTNING-HOLES. 



535 



Thus proving that the glass was not a pure quartz glass. Owing to 

 the small amount of material at his disposal, the other constituents 

 could not he determined. 



As viewed in their sections under the microscope, this glass was 

 completely amorphous, showing only a few partially fused grains on 

 the outer portion. There were no traces of crystallization products 

 from the fused magma, the duration of the heat and the cooling fol- 

 lowing being too brief and too rapid for their productions. It was, 

 however, filled with cavities of varying sizes, formed by the volatiliza- 

 tion of the moisture in the sand at the time of the formation of the tube. 



In the paper by the present writer, already referred to, the composi- 

 tion of both the fulgurite glass and the sand in which they formed is 

 given as follows : 



COSSTITrENTS. 



Ignition 



Silica 



Oxides of iron and aluminium 



Calcium oxide 



Magnesium oxide 



Potassium oxide 



Sodium oxide 



Total 



Glass. 



100-68 



Sand. 



9964 



Thus proving conclusively that, in this case at least, the glass was not 

 a pure quartz glass, although it showed itself to be richer in silica 

 than the sand from which it originated — a result which, to say the 

 least, was hardly expected. 



Discussing the results of the above analyses, the writer concludes 

 that the composition of the fulgui'ite glass is dependent entirely upon 

 the conducting power of the various mineral constituents of the sand, 

 regardless of their fusibility ; that the glass, showing a larger propor- 

 tion of silica than the sand in which it forms, points to the fusion of 

 the siliceous (i. e., the quartz) grains, in preference to the feldspathic 

 and ferruginous ; hence, that the quartz-grains were poorer conduct- 

 ors of the electric fluid than were the others. This may, perhaps, 

 be in part accounted for from the fact that the feldspar-grains were 

 partially kaolinized, and hence held more moisture, which would ren- 

 der them better conductors. 



It is not at all strange that at first many opinions prevailed regard- 

 ing the nature and origin of the fulgurite tubes, and that some of these 

 were peculiar in the extreme. Pastor Hermann seems to have gone 

 farthest astray, for he says : " This growth (i. e., the fulgurite) is un- 

 doubtedly the product of a subterranean fire, whereby not only this 

 tube is formed through melting sand, accedente viscoso quodam fucco, 

 but also the two springs at Massel and Ellgutt, between which this 

 tube is found, are warmed by the same fire." 



