690 



A. A. J U LI EN 



needles, fibers, and granules, in an irregular felted mass, through 

 which obscure circular and elliptical outlines {b, etc.) indicate 

 the position of numerous original bubbles, now flattened, freed 

 from gas, and even partly obliterated. With this darker 

 material, evidently entirely devitrified glass, there occur frequent 



^V^^fev> 



0}^ 'Mr^^M:-^ J> 





$:ft':^ 



^^'ji.W 



^'MW^'^^'^0''^''/i^^W:-^ 













Fig. 3. — Rock-Fulgurite, Wyoming. X 50- Cross-section of contact. 



alternations [d, d, etc.) of thin films of a microscopic breccia or 

 " mylonite," shining brightly between the crossed nicols. This 

 is composed apparently of rock-dust,^ made up chiefly of angu- 

 lar splinters of feldspar ; a few coarser fragments of the same 

 are also irregularly interspersed (/). Along the line of contact 

 {d'), the same angular dust is drawn out in streaks or gathered 



' Apparently related to the opaque whitish layer, between the glass and rock, in 

 the fulgurite of Monte Viso, and referred by Rutley to altered titanite. 



