258 «J. 8. Diller—Fulgurite from Mt. Thielson, Oregon. 
well known that particles electrified by a passing current repel 
each other most forcibly in the direction of the current, and this 
repulsion may perhaps explain the lines of motion in the envel- 
oped fulgurite as well as those which are so prominent parallel 
to the length of the lightning tubes. To the same repulsion 
may be due, at least in part, the accumulation of fulgurite 
about the openings of small tubes upon the surface of the rock. 
In describing such accumulation one author has remarked 
that the tubes seem to have boiled over. The effusion of ful- 
solidifies from a molten magma. The groundmass (last pro- 
Os 
storms presents the most favorable condition for the extensive 
formation of fulgurite. eee 
U. 8. Geol. Survey, Washington, D. C., May 27, 1884. 
