1895.] Prof. Hughes, Exhibition of specimen of Travertine. 17 



Monday, 25 November, 1895. 

 Professor J. J. Thomson, President, in the Chair. 



L. A. Borradaile, B.A., Selwyn College, was elected a Fellow 

 of the Society. 



The following communications were made to the Society : 



(1) Exhibition of a curious specimen of Travertine lining a 

 wooden pipe. By Professor T. McK. Hughes, M.A., F.R.S. 



The interesting specimen exhibited was presented to the 

 Woodwardian Museum by Mr Benjamin Holgate, of Headingley, 

 near Leeds, who has furnished me with the following information 

 respecting it. 



It is a deposit of travertine formed inside a rectangular wooden 

 pipe, used for conveying water from near the surface to the bottom 

 of a mine under Magnesian Limestone. The wood decayed away and 

 was entirely removed, leaving on the surface of the travertine the 

 impression of every detail of the woody structure, so that it looks 

 more like wood replaced than a cast of the interior surface of the 

 pipe. Where a rusty nail projected into the travertine some of the 

 iron scaled off, and the rust stained the deposit for a considerable 

 distance round it so as to increase the deceptive resemblance to 

 sawn timber. 



Another curious point in this specimen is the manner in which 

 there is always a tendency to break along what may be called the 

 miter joints. The deposit is built up in layers parallel to the 

 inside surfaces of the pipe, and when crystallization is set up, 

 the crystals are formed at right angles to those surfaces. The 

 faces of the parallel prisms readily coalesce to form one crystalline 

 mass, but the faces of the pyramids do not so easily unite, espe- 

 cially under conditions in which, owing to the continuously reduced 

 extent of surface, the marginal terminations are imperfectly de- 

 veloped. 



The same phenomenon occurs in iron casting. If the metal 

 cools against an irregular surface, which would tend to cause crys- 

 tallization to start from surfaces arranged at various angles to 

 one another, where the iron crystallized from one surface meets the 

 iron whose fibres of crystallization have originated from another 

 differently inclined surface, these two masses will not coalesce, 

 but a plane of separation will extend some distance into the 

 body, and be a source of weakness though the exterior may have 

 been planed down so that the cause is not obvious. 



VOL. ix. pt. i. 2 



