Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/540

530 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.

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. 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