680 A.. A. JULIEN 



low magnifying power, a faint granulation is discernible through- 

 out the glass. This is resolved under higher power ( X 300) 

 into an irregular, sparse to abundant distribution of crystallites 

 through a predominant glassy base, from the margin of the 

 lumen to the fusion-border of the sand-grains. No special 

 concentration occurs, except in occasional richer wisps and 

 streaks, like diffusion-streams, across minute patches of clearer 

 glass. In general they are scattered in the same .way among 

 and near to the air-vesicles. In some cases, however, an elon- 

 gated vesicle is surrounded by a band of perfectly clear glass, 

 free from microlites, 5 to lO//. in width, which broadens to 20 or 

 30 /u, opposite the ends of the major axis of the vesicle. This 

 has been plainly due to compression and extension of an 

 original envelope of viscid glass, chilled and consolidated by 

 proximity of the vesicle, before devitrification could take place 

 within this envelope. But in general throughout the glass we 

 may recognize one condition that has favored crystallization, in 

 the influence of absorbed vapors, through the abundantly inter- 

 mixed bubbles.^ 



These microlites are straight or curved, sometimes lath- 

 shaped, less than i/x in length in some cloudy aggregates, but 

 largely 3 to 13/*, or even extend into threads, often bent or 

 crooked, 30 or 40 /u. in length. They lie in all positions and 

 never display any fluidal arrangement, "^ though the larger num- 

 ber seem to be radially disposed toward the center of the ful- 

 gurite-tube. Between crossed nicols the microlites exhibit very 

 feeble double refraction, mostly pale gray, here and there 

 brightening into pale greenish-white of the first order. All 

 these forms appear to represent the regeneration of feldspar. A 

 very few margarites were also distinguished, and one spherulite 



' As in the pumiceous glass of the fulgurite of Little Ararat III, as well as in the 

 devitrified glass of Monte Viso, of which Rutley states that the vesicles are sometimes 

 so closely packed that the glass is quite spongy. However, the pumiceous glass of 

 other fulgurites has been found entirely homogeneous. 



^ In fulgurite-lumps from Florida, Merrill recognized a fluidal structure in the 

 homogeneous glass near bubbles, "as if by sudden expansion of a steam-bubble in 

 the plastic material " (loc. cit., p, 87). 



