STUDY OF STRUCTURE OF FULGURITES 693 



of microlites, in every instance, in the series I have examined, 

 seems at first somewhat at variance with the conclusions of 

 Lagorio as to the particularly difificult saturation of a molten 

 silicate by the oxides represented in that mineral. But we have 

 here, apparently, a far different magma from that employed in 

 the experiments of Pelouze, artificial glass, /'. e., from every evi- 

 dence, a supersaturated solution of feldspar in its own fused 

 material. In such a magma-solution, a combination of silica, 

 alumina, and alkali molecules, must find conditions highly favor- 

 ing ease and rapidity in re-crystallization. 



Alexis A. Julien. 

 Columbia University, 

 New York City. 



EXPLANATION OF FIGURES 



Fig. I . Sand- Fulgurite , Poland. — ■ Photomicrograph of cross-section, 

 showing sharply defined outline of central lumen, the glass wall with its 

 vesicles, and ring of dark semi-fused sand-grains, adhering to the irregular 

 outer boundary of the fulgurite. X 10. 



Fig. 2. The same. — Photomicrograph of section of part of the wall, 

 showing forms, radial distension, and distribution of the vesicles, the smaller 

 and darker ones still occupied by air. Several of the sand-grains appear 

 along the outer boundary, each with its inner crescent of limpid glass. The 

 inner dark part of a grain indicates the side which has been partly fused ; 

 the outer clear part, that which remains unaltered. X50. 



Fig. J. Rock-Fulgiirite, Central Butte, Wyoming. — Drawing of cross- 

 section, showing line of contact {d' , h, c' , e) between phonolite, p, and 

 fulgurite, a. 



b. Obscure flattened vesicles. 



c-c' . Carlsbad twin of orthoclase, with shattered ends, surrounded by 

 feldspar-dust and devitrified glass, enclosing a few bubbles. 



d, d, d. Films of rock-dust, alternating with laminae of devitrified glass. 

 d' . Film of rock-dust along the contact. 



e, Projecting corner of feldspar-grain, shattered by the electric current. 



f, etc. Feldspar fragments scattered through the fulgurite. 



h. Green hornblende needle, unaffected by the fulgurite-stream. X50. 



