A STUDY OF THE STRUCTURE OF FULGURITES. 



Some obscure problems in structures occurring within artifi- 

 cial and natural glasses (rhyolites, tachylites, etc.) receive light 

 from the study of fulgurites, as representatives of instantaneous 

 fusion, and frequently, as it will be shown, of equally rapid 

 devitrification. 



Hitherto, however, a constitution of homogeneous glass has 

 been universally observed, under the microscope, in all sand- 

 fulgurites, without the least trace of devitrification in the largest 

 masses.' Occasional cloudy stains of brown iron-oxide and 

 black manganese-oxide have been noted, and frequent enclosure 

 of remnants of quartz-grains "^ and of bubbles, both more abund- 

 ant near the outer walls of fulgurite. 3 In rock-fulgurites, a 

 single instance of devitrification has been recorded. The results 

 of examination of four fulgurites will now be described. 



I. Fulgurite (lightning-tube) from sand, Poland; 'a small 

 fragment, together with thin cross-sections, prepared by Mr. 

 James Walker, of the New York Microscopical Society. This 

 fulgurite is of small size, from 5 to 8""" in diameter, with central 

 aperture or lumen usually 2.5 to 4"™ in diameter, and glass wall 

 varying mostly from 0.6 to 2.0™"^ in thickness, roughened out- 

 wardly by adhering sand-grains in a continuous coating. The 

 photomicrographs (Figs, i and 2) may serve to explain certain 

 features as yet unrecognized in other fulgurites. 



The wall presents, under low magnifying power, an appa- 

 rently homogeneous glass, streaked by occasional cloudy wisps 



'"A Perfect Glass," Arago {Ann. d. Ch. et. d. F/iys., Vol. XIX (1821), p. 290) 

 and all later investigators. 



= Von GiJMBEL, Zeits. d. D. geol. Ges., Vol. XXXIV (1882), pp. 647-648. 



J. S. DiLLER, Am.Jozir. Sci., Vol. XXVIII (1884), pp. 252-258. 



G. P. Merrill, Proc U. S. Nat. Mus. (1886), p. 84. 



3 Best shown in the longitudinal and cross-sections of a sand-fulgurite by A. 

 WiCHMANN {Zeils. d. D. geol. Ges., Vol. XXXV (1883), PL XXVIII). 



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