co MALDONADO. [cHap. 111 
tubes projected above the surface; and numerous fragments 
lying near, showed that they had formerly been buried to a 
greater depth. Four sets entered the sand perpendicularly’: by 
working with my hands I traced one of them two feet deep; and 
some fragments which evidently had belonged to the same ‘tube, 
when added to the other part, measured five feet three inches. 
The diameter of the whole tube was nearly equal, and therefore 
we must suppose that originally it extended to a much greater 
depth. These dimensions are however small, compared to those 
of the tubes from Drigg, one of which was traced to a depth of 
not Jess than thirty feet. : 
The internal surface is completely vitrified, glossy, and smooth. 
A small fragment examined under the microscope appeared, 
from the number of minute entangled air or perhaps steam 
bubbles, like an assay fused before the blowpipe. The sand is 
entirely, or in greater part, siliceous; but some points are of a 
black colour, and from their glossy surface possess a metallic 
lustre. The thickness of the wall of the tube varies from a 
thirtieth to a twentieth of an inch, and occasionally even equals 
atenth. On the outside the grains of sand are rounded, and 
have a slightly glazed appearance: I could not distinguish any 
signs of crystallization. In a similar manner to that described 
in the Geological Transactions, the tubes are generally com- 
pressed, and have deep longitudinal furrows, so as closely to 
resemble a shrivelled vegetable stalk, or the bark of the elm or 
cork tree. Their circumference is about two inches, but in 
some fragments, which are cylindrical and without any furrows, 
it isas much as four inches. The compression from the surround- 
ing loose sand, acting while the tube was still softened from the 
effects of the intense heat, has evidently caused the creases or 
furrows. Judging from the uncompressed fragments, the mea- 
sure or bore of the lightning (if such a term may be used), must 
have been about one inch and aquarter. At Paris, M. Hachette 
and M. Beudant* succeeded in making tubes, in most respects 
similar to these fulgurites, by passing very strong shocks of 
galvanism through finely-powdered glass: when salt was added, 
80 as to increase its fusibility, the tubes were larger in every 
* Annales de Chimie et dv Physique, tom. xxxvii,, p. 319. * 
