254 JS. 8. Diller—Fulgurite from Mt. Thielson, Oregon. 
purely superficial coating, and not in the form of lightning- 
tubes. It has also been observed in connection with phono- 
lite (?) (Klingstein porphyr) in the Auvergne; and Hum- 
boldt found it on one of the very acute volcanic mountains 
of Mexico, where it had resulted from the fusion of “ reddish 
trachytic porphry ” (andesite ?). The summit, like that of Mt. 
ielson, is very small and precipitous, and the vesicular, 
hole. The rock is porous and at places even spongy. +1 
cavities are lined with minute clear colorless crystals and it 
pears evident that this structure has not been produced a 
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ceous and its interior is brightly glazed. The hardness of the 
fulgurite is a little below that of ordinary glass. It is rather 
tough, strongly lustrous, and has a specific gravity of about 2. 
In the flame of an alcohol lamp thin splinters readily fuse with- 
out intumescence. The groundmass of the rock fuses much less 
readily than the fulgurite to a very dark glass. Small frag: 
~ments of the fulgurite when heated become strongly magnetic. 
It appears to be entirely insoluble in strong acids, eve? 1? 
aqua-regia, and is not affected by boiling solutions of potassium 
