152 r. ETJTLET OX FrLGrEITE FEOil MON'T BLANC. 



19. On Fttlgtibite from Mont Blanc ; i«;ziA a JSTote o>i f^e Botjteil- 



LENSTEIN", or PsEFDO-CHETSOLlTE of MoLDATJTHEIN', in BoHEJDA. 



By Fkank Etjtlet, Esq., F.G.S. (Eead January 25, 1885.) 



[Plate ni.] 



An interesting paper by Mr. J. S. Diller, of tlie United-States 

 Geological Survey, upon fulgurite from Mt. Thielson in Oregon, 

 appeared in the ' American Journal of Science,' vol. xxviii. Oct. 1884, 

 in which allusion was made to the effect of lightning upon horn- 

 blende-schist on the summit of Mont Blanc, as noted by De Saussure. 

 On reading this, I remembered that some years ago Mr. James 

 Eccles gave me two or three small specimens showing evidence 

 of fusion on their surfaces, which he at the time considered to 

 be due to the action of lightning. They were collected by him on 

 the summit of the Dom du Groute from smaU peaks of rock rising 

 out of the snow at a height of 14,000 feet above the sea-level. 

 These peaks form part of the chain of Mont Blanc. The fragments 

 are small and consist of hornblende gneiss ; for they contain some 

 felspar, and one of the specimens is traversed by coarse irregular 

 foliations of felspar. Mr. Cuttell has made several attempts to 

 prepare a section through this specimen with the thin fulgurite film 

 adhering to it, but unfortunately failed, the fulgurite crumbling 

 away in each trial. The cuts made through the specimen at various 

 points show, however, that the fulgurite is quite superficial, no 

 trace of fusion being visible below the original surface when the 

 cut surfaces are examined with a lens. Indeed there appears to be 

 no alteration of the rock from the electric fiash, except on the 

 actual surface itself, where a number of globules, sometimes in the 

 form of attached spheres, sometimes in quite irregularly fused pellets 

 and blotches of brownish-black and of white glass, have been formed. 

 The latter is the frothy glass or enamel resulting from the fusion of 

 felspar, while the dark glass is due to the fusion of hornblende. 

 Upon one piece the surface is fretted and blistered over an area of 

 about half a square inch. Some of the globules have minute holes 

 from which gas has escaped ; while others have been inflated into 

 thin, spherical, or irregularly blistered bubbles (PI. III. fig. 1). 

 The dark glass is tough, some pressure being needed in order to 

 detach small pieces from the broken bubbles, fragments of these 

 bubbles, when examined under the microscope with high powers, 

 appear to be absolutely structureless and to contain nothing but a 

 few small gas -bubbles (PL III. fig. 2). In this respect the glass 

 corresponds precisely with the Mt. Thielson fulgurite described by 

 Mr. Diller, for there is no trace of cystallization-products in either 

 case. PL III. fig. 4 represents an elongated and twisted glass 

 enclosure containing many gas-bubbles. It occurs in a fragment 

 of the fulgurite. On the surface of one of the specimens three or 

 four glass-bubbles, each about the eighth of an inch in diameter, adhere 



