364 



Dr. F. Clowes. 



[June 20, 



by geologists as the Keuper basement beds of the Trias. But no 

 satisfactory explanation has yet been given of the power possessed by 

 these bold elevations to resist the denudation which has removed the 

 surrounding deposit. 



An analysis of a sample of sandstone from the top of the Hemlock 

 Stone was made a few years since by H. F. Blake and A. P. Beddard, 

 then students in my laboratory. They detected a large amount of 

 barium sulphate in a crystalline condition, inclosing and binding 

 together the grains of sand. This appeared to furnish a clue to the 

 cause of the resistent power possessed by the stone. In the company 

 of Professor Blake, I proceeded accordingly to collect specimens of 

 the sandstone present at different levels of the Hemlock Stone and 

 of the two adjacent hills, and to subject them to qualitative analysis. 



Qualitative Composition. — The cap of the Hemlock Stone was 

 found to be free from carbonates and from calcium, and contained 

 much barium sulphate ; the stone was compact and hard. The soft 

 loose sandstone at certain lower levels, however, contained some 

 calcium sulphate and a variable proportion of calcium carbonate, the 

 barium sulphate being in much smaller quantity than in the top ; 

 sodium was also present in fair proportion. The resistent power 

 conferred by the almost insoluble barium sulphate upon the top of 

 the stone would probably explain its projecting cap-like shape, the 

 lower portions having suffered by weathering to a far larger extent, 

 owing to the more soluble nature of the calcium compounds which 

 they contained, and to the smaller proportion of the barium 

 sulphate. 



The sandstone of which Bramcote Hill is composed showed a 

 variation in chemical composition similar to that of the Hemlock 

 Stone. The sandstone at the summit of the hill was free from 

 carbonates, and contained much barium sulphate ; this was the 

 general character of the stone at lower levels, but one sample, taken 

 about half-way up the hill, contained calcium carbonate and a less 

 proportion of barium sulphate. 



Stapleford Hill, on the other hand, showed throughout an absence 

 of carbonates and of calcium, while barium sulphate was always 

 present, and usually in quantity. 



Distribution of the Barium Sulphate. 



In certain portions of the sandstone the barium sulphate is evenly 

 distributed throughout the mass of the rock, giving on fracture a 

 surface of compact and uniform appearance. In other portions the 

 sulphate is seen on the surface produced by fracture as a network of 

 light-coloured compact veins inclosing darker and more or less loose 

 sand grains; the weathered surface in this case presents a honey- 



