Page:Popular Science Monthly Volume 30.djvu/555

 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 be 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 following being too brief and too rapid for their productions. It was, however, filled with cavities of varying sizes, formed by the volatilization 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 composition of both the fulgurite glass and the sand in which they formed is given as follows:

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 fulgurite 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 proportion 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 conductors 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 render them better conductors.

It is not at all strange that at first many opinions prevailed regarding 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 undoubtedly 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."