366 



Dr. F. Clowes. 



[June 20, 





No. 1. 



No. 2. 





0-21 

 0-87 



0-21 

 1 -60 



In solution in HC1 : — 



Fe.0 3 + AL0 3 



CaO 



0-97 



o-oo 



- 13 

 0-66 

 0-85 



2-34 



1 -oi 



22 



1 20 

 1-33 



Mo-O 



SiO, 



Alkalis, &c. (by difference) . 





96-31 



92 -09 



It may be assumed that the loss which the sandstone suffers by 

 long treatment in the form of powder with dilute hydrochloric acid, 

 will be greater than that caused by very long weathering, since the 

 hot acid is a more powerful solvent than rain-water, and it is further 

 enabled to attack the whole mass of the stone instead of the surface 

 only. Under these extreme conditions, however, the stone forming 

 the cap of the Hemlock Stone lost only 3*7 per cent, of its weight. 

 Its protective power as an unwasting cover over the column beneath 

 is therefore easily understood. The whole substance of the two hills 

 will evidently behave in a similar way to the top of the Hemlock 

 Stone, and render them practically permanent under the action of 

 weathering. 



Microscopic Examination. — Professor Lebour kindly undertook the 

 microscopic examination of a fine section of this sandstone, prepared 

 by Mr. Gr. Healey. He reports 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 include narrow, rod-like crystals, 

 which in all likelihood are apatite." 



Occurrence of Barium Suljpliate in other Sandstones. 



The occurrence of barium sulphate in British sandstones has not 

 been hitherto noticed ; this at least was the verdict of the geologists 

 assembled at the British Association meeting at Aberdeen, before 

 whom a preliminary announcement of the discovery was made (' Brit. 

 Assoc. Report, 5 1885, p. 1038). 



A careful examination of a large number of specimens of sandstone 

 from the neighbourhood of Nottingham, and from other parts of the 

 country, has confirmed this verdict. I have in no case found even a 

 trace of any barium compound. Mr. H. T. Brown, F.R.S., however, 



