Transactions of the Geological Society, 1st series, vol. 2/On the vitreous Tubes found near Drigg, in Cumberland
XXIV. On the Vitreous tubes found near to Drigg, in Cumberland
Compiled by the Secretaries from several Communications.
IN the hillocks of drifted sand, which lie between the mouth of the river Irt and the sea near to Drigg, in Cumberland, hollow tubes of a vitreous substance were discovered rising above the surface perpendicularly through the sand.[1] They were found three in number, within an area of fifteen yards, upon a single hillock, about forty feet above the level of the sea. The diameter of each was about an inch and a half. An excavation being made around one of them, it was found to descend perpendicularly through the sand about thirty feet. At the depth of about twenty-nine feet the sand was interrupted by a bed of pebbles, appearing to be the continuation of the sea-beach. The tube here came in contact with a fragment of hornstone-porphyry, glanced off from it at an angle making about 45° with the horizon, and then returned to its former vertical position. Below this fragment the tube, becoming extremely delicate, was frequently broken; and at the distance of a foot, during 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 the exterior, and the whole tube has the appearance of being creased by compression, while in a soft state. The opposite sides of a crease are often brought into contact and welded together, and thus the tube is sometimes so flattened as to be entirely closed. In this way the irregular furrows on the outside have been produced.
The tube on touching the pebble of hornstone porphyry above mentioned, was welded to it; but on the side adjacent to the pebble the substance of the tube was wanting, and in the place of it was found an unglazed rust-coloured mark, passing across one of the flat faces of the stone. In parts of this mark thin laminæ were standing up from the surface, and two small patches of an olive coloured glass were adhering to the edges of two natural fissures in the pebble.[2]
Since the substances that have been described had all the marks of fusion, it was not improbable that they might be imitated by submitting to the action of heat the sand and the pebble with which the tube came in contact. With this view the following experiments were made.
A fragment of the pebble, of a greenish slate colour, heated to a dull red before the blowpipe, became rust-coloured, and when urged by a strong flame, was melted into an olive-coloured glass, similar to that observed on the surface of the pebble.
The sand of which the hillocks are composed, viewed through a lens, appears to consist of grains of white or reddish quartz, mingled with a few grains of hornstone porphyry.[3] The latter, when picked out of the sand, are fusible before the blowpipe like the pebble of the same substance, but they are not in sufficient quantity to act as a flux on the entire sand heated in the usual manner. The sand so treated is reddened in the first instance, changes afterwards to an opaque white, and finally is very slightly agglutinated, resembling in its shades of colour and in its cohesion that which adheres to the outermost coating of the tube.
The sand was exposed to the flame of a spirit lamp, urged by a stream of oxygen gas, in which flame Dr. Marcet has shewn that a thick wire of platina may be melted. The grains of hornstone porphyry first began to flow, and presently acting upon the grains of quartz, formed a clear glass mingled with portions of an olive colour. Even thus however the fusion was partial, and the utmost intensity of the flame was required to support it.
The glass thus formed resembled that of the tube in its external characters, in being very hard and difficult of fusion, and in containing a great excess of siliceous matter: for it was ascertained that a fragment of the tube was scarcely softened at the edges by the same flame that had melted the sand; and that the substance of the tube contained a large portion of silica, had been determined by one of the members.
From what has been stated, it appears that the tubes have all the marks of fusion, and that their substance can be imitated in some measure by subjecting the sand to intense heat. That they are of very recent date is certain from the shifting nature of the sand hillocks in which they are found, and from their inability to remain alone and unsupported by the sand without breaking. Lightning seems to be the only agent that could at once supply the heat and the force requisite to make them. In the familiar experiment of perforating a quire of paper by the Leyden battery, a mechanical effect of electricity analogous to the present is exhibited, and instances of fusion by the same instrument it is not necessary to enumerate.
The sand hillocks of Drigg, though of inconsiderable elevation, are not unfavourably situated for promoting a discharge, since they present themselves as the first and highest object in front of the marshes of the Irt to clouds coming from the sea. Should the explanation of the Sand Tubes, which is now offered, be admitted, some judgment may be formed of the intensity of the heat developed in great electrical explosions.
- ↑ The first notice of these substances was transmitted to the Society in the year 1812 by E. L. Irton, Esq. of Irton Hall, in Cumberland, and was accompanied by specimens. This gentleman removed the sand from around one of the tubes to the depth of 15 feet. Messrs. Greenough and Buckland, Members of the Society, examined the sand hills in company with Mr. Irton in the autumn of the year 1813, and finding the surface lowered more than 15 feet by drifting since the year 1812, resumed the excavation. The observations of these three gentlemen are introduced into the present paper.
- ↑ A similar appearance is noticed by Saussure (1153) on the Dome de Gouté, and is by him referred to the action of lightning. The pebble above mentioned is in the cabinet of the Society; the adhering tube was unfortunately broken off in its way to London.
- ↑ A few fragments of shell are also to be seen here and there.