684 A. A. J U LI EN 



II. Fulgurite on gneiss, near Split Rock, Lake Chaniplain, New 

 York; specimen collected by Professor William Hallock, of 

 Columbia University, immediately after the lightning-stroke, as 

 described in his accompanying article. Thin sections of this 

 granite-gneiss were prepared, one in plane parallel to and within 

 about 0.03'"" of the fulguritic crust, the other in cross-section. 

 The rock is found to present a surface somewhat dulled by 

 weathering, and to consist, to about 70 per cent, of its volume, 

 of feldspars, microcline, microperthitic orthoclase and a little 

 plagioclase, besides much quartz and a small amount of mag- 

 netite, biotite, garnet, and rutile, but no trace of fulguritic glass. 

 No undulatorv extinction occurs between the nicols, as evidence 

 of strain. 



The fulgurite-pellicle is entirely superficial,^ brittle, and with 

 slight adherence to the rock, from o.i to 0.3™" in thickness, 

 nearly white, consisting chiefly of a minutely blebby hyaline 

 crust with blistered, glistening surface, whose bubbles, rarely 

 exceeding 0.2"^™ in diameter, are nearly spherical but somewhat 

 elongated normally to the surface of the rock. On careful 

 examination of these, in a flake mounted in balsam, under a 

 good tenth-inch immersion objective, no water of condensation 

 could be detected in any vesicle. 



Many short glass- fibers occur, sometimes with globular ends, 

 resembling some of those in " Pele's Hair" from the crater of 

 Kilauea, Hawaii. This white pumiceous slag is quite uniformly 

 attached to the predominant surfaces of feldspar, though pierced 

 by the uncovered gray grains of quartz. It is dispersed over 

 the rather even surface of the hard gneiss in radial, somewhat 

 dendritic forms, often many inches in length, thinning out into 

 feathery fleeces at the margins. Wherever these pass over 

 minute plates and seams of the dark minerals of the rock, the 

 blebby fulgurite assume a yellow, red, brown, or black color, as 

 a dark enamel, or in the form of tiny spherules.^ 



' Similar superficial films of fulgurite have been often observed, by Humboldt in 

 Mexico, by Brun in the Alps, by Ramond on mica-schist, on limestone, and on phon- 

 olite in the Pyrenees and Auvergne. 



2 Over the fulgurite-crust on hornblende-gneiss at Mount Blanc distinct white and 



