18 



J. A. PHILLIPS ON THE CONSTITUTION AND 



Water J h yg rometric 3 * 85 



[ combined. . . . , 6-56 



Silica 49-81 



Phosphoric anhydride 0*42 



Alumina 5*17 



Ferric oxide 29-17 



Ferrous oxide 0*35 



Lime 2-43 



Magnesia 0-95 



Potassa 0-48 



Soda 0-84 



100-03 



Another variety of this rock from the same locality, but darker 

 in colour, was found to contain 37 per cent, of ferric oxide and 45 

 per cent, of silica ; the amount of phosphoric anhydride was nearly 

 the same as in the first specimen analyzed. 



An examination of the spherules of various pisolitic iron-ores 

 shows that they exhibit all the characteristics of the globular 

 ferruginous grains found in these sandstones ; and it may therefore 

 be inferred that they have had a similar origin. A pisolitic iron- 

 ore of Middle JSTeocomian age, which occurs at Market Rasen in 

 Lincolnshire, consists to a large extent of spherules very closely 

 resembling the ferruginous graias in the sandstones at Hunstanton. 



Tertiary. — Hertfordshire Puddingstone, Lower Eocene, is a conglo- 

 merate of flint pebbles united by a concrete consisting of fragments 

 of transparent quartz and greyish flint held together by a flinty 

 cement. In this concrete the quartz is considerably in excess of 

 the flint, and sometimes contains fluid-cavities. Its fragments are 

 all angular, and vary in diameter from to inch. 



A specimen of sand from Hordwell, Hampshire, equivalent in age 

 to the Headon beds, contains no recognizable felspar. All the quartz 

 down to a diameter of ^ inch is completely rounded ; and even the 

 smallest particles have had their angles entirely removed. Fluid- 

 cavities with bubbles are abundant in some of the quartz consti- 

 tuting this sand. 



Sand from the Marine beds, near the top of the Hempstead series, 

 Isle of Wight, was, after treatment with hydrochloric acid, found to 

 be composed chiefly of grains of quartz, of which about three 

 fourths had a diameter of less than inch. These, down to the 

 finest particles, are much rounded, although still roughly retaining 

 the form of the original fragments. 



The fine-grained brilliantly coloured sands at Alum Bay, Isle of 

 Wight, of Upper Eocene age, usually classified as Lower Bagshot, 

 have not, as yet, been definitely identified with the beds of the London 

 Basin. By digestion in hydrochloric acid the quartz becomes colour- 

 less ; and, although not completely rounded, the angles even of the 

 smallest fragments have generally been modified by attrition. Fluid- 

 cavities are not plentiful, and when present seldom enclose bubbles. 



