Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/539

From Wikisource
Jump to navigation Jump to search
This page has been validated.
On the Vitreous tubes found near Drigg, in Cumberland.

an attempt to recover it, the sand fell in and prevented further investigation. The lowest part of the last piece, that was detached, was not closed, and did not exhibit any peculiarity of structure, from which it could be inferred that the extremity had been reached. The tube appears to have tapered in its descent, its diameter at the bottom of the excavation being reduced to half an inch. One specimen in the collection of the Society is bi-furcated; whence it is probable, that the stem was divided into two branches, one of which may have escaped observation. Small lateral branches proceeded from different parts of the stem, not exceeding two or three inches in length, nor a quarter of an inch in diameter at the points of insertion. They were conical, and ended in points, gradually bending downwards. Internally they were hollow, and opened into the principal duct, which, except in dimensions, they perfectly resembled.

The outside of the tube is coated with an agglutinated sand, which viewed with a lens is found to consist of black and opaque white grains mixed together, and rounded, as if by incipient fusion; the white grains, when farthest from the centre of the tube, having a reddish tint. The stem is irregularly angular, like a vegetable stalk much contracted by drying, and is rugged with deep longitudinal interrupted furrows, like the bark of the elm or of the cork tree. The sides of the tube are about the twentieth part of an inch thick, and are very hard and rigid.

On proceeding inwards, their substance gradually loses the appearance of sand, and becomes vitreous, the whole interior being covered with a smooth glaze. This vitrified matter is whitish or limpid, containing specks of a dark olive colour and a few air blebs. It is sufficiently hard to scratch glass.

The irregular form of the interior surface corresponds to that of

Vol. II.3 x