TRANSACTIONS OF SECTION C. 



595 



sulphate.' This sandstone occurred over a consitlerable area, and formed the 

 liraracote and Stapleford Hills, as well as the pillar of rock known as thd Hemlock 

 Stone. The occurrence of this insoluble cenientinp material was held to account 

 for the re-istance to denudation which had given rise to the above-mentioned pro- 

 minences. Since communicating the above paper, full quantitative analyses oi 

 specimens of this sandstone have been made, with the following results : — 



A further examination made to ascertain the loss which the finely-powdered 

 sandstone sufl'ered when heated with dilute hydrochloric acid gave the following 

 I'esults; — 



The small loss of 3-7 per cent, suffered by the sandstone under this severe treat- 

 ment fully confirms the idea that this stone must lose by weathering with extreme 

 slowness. 



Professor Lebour kindly undertook a microscopic examination of a fine section 

 of the sandstone prepared by Mr. G. Healey. He reported that ' the cementing 

 material is undoubtedly crystalline barium sulphate,' and that ' besides the quartz 

 grains, there are others of much the same average size and shape, the nature of 

 which is not clear.' The quartz grains are 'more angular than rounded, and in- 

 clude narrow, rod-like crystals, which in all likelihood are apatite.' 



The occurrence of barium sulphate as a cementing material in Briti.sh sandstone 

 lias not been previously proved with certainty, although Mr. Aubrey Strahan, B.A., 

 suspected its presence in the rock of Beeston Castle, (Jhesliire.- Mr. H. T. Brown, 

 F.li.S., however, after examining specimens of the Beeston Castle rock in his pos- 



' lirit. Assoc. Rfport, 1885, p. 1038. 

 * Geol. Survey Memoirs, 1882, pp. 7, 8. 



Q Q 2 



