530 On the Vitreous Tubes found near Drlgg^ in Cumberland. 



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 furroM-^s 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 Hat 

 faces of the stone. In parts of this mark thin laminse 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 sub- 

 mitting 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, f 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 



* A similar appearance is noticed by Saussiire C1153) on the Dome de Gou^e, and is 

 by him referi( d to the action of lightning. The pebble above mentioned is in tl;e cabinet 

 of the Society ; the adhering tube was unfortunately broken off in its way to London. 



t A few fragments of shell are also to be seen here and there. 



