These dimensions are however small, compared to those of the tubes from Drigg, one of which was traced to a depth of not less 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 a tenth.

On the outside the grains of sand are rounded, and have a slightly glazed appearance: I could not distinguish any signs of crystallisation.