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fn ME Se dee ae 
a. That the fulgurite is formed chiefly by the fusion of the 
groundmass of the rock is shown clearly also by the following 
chemical analysis made by Professor Clarke and Dr. Chatard in 
the laboratory of the U. S. Geological Survey. The amount of 
fulgurite obtainable from the hand specimens was very small 
and sufficient for only a partial analysis. The alumina and — 
iron were estimated together, and the amounts of potash and 
d 
soda were not determined. 
Fulgurite. Groundmass. 
Silica (SiO, 55°04 55°85 
Alumina (Al,O, 98-99 22°95 
Ferric oxide (Fe,O,) t 4°59 
Lime (CaO) 7°86 8°41 
Magnesia (MgO) 5°85 3°08 
Potash (K,O) 2°67 
Soda (Na,O) 2°16 
Loss by ignition Tt 0°52 
98°85 100°23 
The groundmass was separated from the olivine, hypersthene, 
and all but a trace of the feldspar by means of Thoulet’s 
Solution, and the magnetite was removed from it by hydrochloric 
acid. The presence of a larger proportion of magnesia in the 
fulgurite indicates the fusion of some of the hypersthene. 
Nearly all of the fulgurite is either superficial or confined 
- to the lining of preéxisting cavities. This is what we should 
expect from the well known fact that electricity always spreads 
itself upon the surface of a body. A small portion of the ful- 
8urite, however, seems to have been produced within the adjoin- 
ng compact rock by fusing the groundmass. It occurs in small 
regular nodules or strings, frequently full of bubbles and ocea- 
Slonally possessing a distinct fluidal structure approximately 
Parallel to the course of the electric current. It is difficult to 
Conceive how a distinct fluidal structure mey have been pro- 
duced in these small masses, which were but momentarily 
Viscous and completely hemmed in upon all sides, unless it 1s 
ue to the repulsion of the particles among themselves. It is 
