688 A. A. JULIEN 



lined or filled with the dark glass, which seem clearly to owe 

 their perforation to the action of electric discharges upon more 

 disintegrated blocks of the crumbling rock. 



The glass is found to be rich in bubbles, especially toward 

 and near the surface of the inner rock-wall, and in places even 

 blown up into blebs and blisters. All of the smaller vesicles and 

 most of the larger are approximately spherical. In none of 

 these could any water of condensation be discovered under a 

 tenth- inch objective; their contents appear to be entirely gas- 

 eous, i. e., chiefly derived, in all probability, from expansion of 

 air rather than steam. Many of the larger vesicles present a 

 more or less elongated form, with major axis always arranged in 

 position at right angles to the adjacent rock-wall. This distor- 

 tion of vesicles in the glass of a rock-fulgurite may be always 

 attributed, in my opinion, entirely to the reaction of pressure 

 inward, i. e., toward the lumen, which has instantaneously fol- 

 lowed the passage of the electric discharge, mainly from expan- 

 sion of the collected bubbles, partly from increased volume of 

 the glass during fusion of the rock. 



When crushed splinters of the glass are examined, though 

 found sometimes entirely amorphous, as reported by Wichmann 

 and others, it is also in places rich in bunches of stony matter, 

 isolated needles (with bright interference-colors between crossed 

 nicols and parallel extinction) and clusters of microlitic fibers, 

 sometimes radiating around a bubble. 



Again, at the line of contact between this glass and the ande- 

 site-wall, an intermediate stony layer occurs, 0.15 to 0.70™™ in 

 thickness, containing a few obscure outlines of bubbles. This 

 plainly consists of wholly devitrified glass, made up of a felt of 

 irregularly crossing needles, fibrous curved wisps, or straight 

 bundles, some rectangular in form, 0.08 to 0.20™™ in length, 

 whose axes lie mostly parallel to the line of contact with the 

 adjacent rock-wall. In the straight bundles an extinction-angle 

 of about 19° is uniformly obtained, often with undulatory phase, 

 and all offer the characteristics of orthoclase. There is a remark- 

 able resemblance, if not identity, of these fibrous aggregates, in 



