STUDY OF STRUCTURE OF FULGURITES 677 



elongated vesicles are in general disposed radially' toward the 

 lumen of the tube, though occasionally one may lie obliquely or 

 even at right angles to that direction, as if twisted around by a 

 sudden thrust. All the facts seem to point to strong lateral or 

 tangential compression of the vesicles within the surrounding 

 glass wall, and to their consequent extension and distortion in 

 the direction of relief.^ 



The sudden expansion of air and vapor by the electric dis- 

 charge has thus effected the dilatation of the lumen, the genera- 

 tion of bubbles throughout the fused glass, and the coalescence 

 of those first formed into the larger vesicles. The relief of this 

 tension outwardly, toward the margin of the tube, first caused 

 the radial elongation of the larger vesicles and extension of 

 conical projections and wings from outer side of the plastic tube, 

 aided, doubtless, by lateral offshoots of the electric current.^ 

 Then, in the moments succeeding the passage of the main cur- 

 rent, the effects of sudden condensation, lateral contraction and 

 recoil are shown in the instances of partial collapse of the tube, 

 in the reverted distortion of vesicles, /. e., inwardly toward the 

 lumen, and in explosion of some bubbles nearest the lumen into 

 pustules and points of glass over its surface. Where the glass 

 retained its plasticity longer, the vesicles have recovered their 

 normal spherical form ; this condition seems to have been 

 regained in nearly all fulgurites whose vesicles have been care- 

 fully examined by others. It is to be noted that elongated 

 vesicles in radial position have been recorded in only two cases 

 of rock-fulgurites, in both within partially devitrified glass, as 

 found in one by Rutley and in the other by Wichmann ; in the 

 latter case (viz., fulgurite III, beyond) I have made the same 



' A position already recognized in other fulgurites by Wichmann and Rutley. 



^One writer considers "this radial arrangement .... possibly indicative of a 

 rudimentary crystallization in the fulgurite glass" (Richardson, Min. Collector, Vol. 

 Ill (1896), p. 132). 



3 Merrill, loc. cit., 87. One consequence of these offshoots, and of the ozonized 

 atmosphere thereby developed, is shown in the reddish stains, due to oxidation of 

 iron, in the sand surrounding a fulgurite, to the distance of 3 or 4 inches; e.g., in that 

 found near Starczynow, Poland (Roemer, N.Jahrb.f. Min., 1876, pp. 33-40). 



