740 MB. J. LOMAS ON THE INOEGANIC [Nov. IpOOy 



The abundance of glauconite in the Crag makes it highly 

 probable, as suggested by M. Van den Broeck, 1 that the decomposi- 

 tion of this mineral is the main source of the iron-oxide which 

 forms the staining-material of these beds. 



In all places where the Red Crag is exposed, it is seen to be 

 composed of a loose shelly sand. Pebbles occur sporadically, 

 ranging up to 3 or 4 inches in diameter. 2 Flint-pebbles are by far 

 the commonest ; they are usually very well rounded. A peculiar 

 hard, brown chalk also occurs along with the flints. Other pebbles 

 consist of pink quartzite, chert, and phosphatic nodules. Rolled 

 clay-galls are found abundantly in most localities, coated with sand- 

 grains, and resembling exactly those which are now being formed 

 on sandy beaches bordering clay-cliffs. 



Rolled specimens of a fairly coarse dark brown sandstone may be 

 collected throughout the series, and can be matched with the Diestian 

 Sandstones of Kent. It is not uncommon to find these pebbles bored 

 by molluscs. 



A finer-grained dark sandstone also occurs, which contains an 

 abundance of mica. This may be the ' mica-schist ' recorded by the 

 late John Brown, of Stanway, as occurring at Beaumont. 3 



The chief object of this communication, however, is to record the 

 rarer constituents to be found in the Crag sands. 



In order to concentrate the rarer minerals, the sands were frac- 

 tionated by means of high-density fluids. At first dilute hydro- 

 chloric acid was used, to get rid of the carbonates and to remove 

 the iron-staining from the grains. It was found necessary, how- 

 ever, to treat the material with hot concentrated hydrochloric acid 

 in order to clear the grains for examination. Even prolonged 

 boiling in strong hydrochloric acid was not sufficient for the black 

 material from Beaumont. Possibly some of the minerals readily 

 soluble in hydrochloric acid have been removed by this treatment. 



Twenty-five grammes of ordinary Red Crag from Beaumont was 

 treated with concentrated hydrochloric acid. The insoluble part 

 was then divided into fractions by means of Rohrbach's solution: — 



•102 gramme, or '4 per cent., had a density greater than 2'7 ; 

 •622 „ or 2-5 „ „ „ less than 25; 



while 12-25 grammes, or 49 „ „ ,, between 25 & 2*7. 



1 ' Du Role de l'lnfiltration des Eaux Meteoriques dans l'Alteration des 

 Depots superficiels' Intemat. Geol. Congr. (Paris, 1878) Comptes Rendus, 

 p. 188. 



2 A block of flint, cubical in shape and 15 inches across, may be seen 

 lying on the floor of the large pit near Sutton Windmill; and Mr. Harmer 

 states that he met with two or three large unworn flints, weighing 10 or 

 12 lbs., at Oakley. 



3 He also enumerates agate, chert, septaria, quartz (milky variety), quartz 

 (highly crystalline like that of the Lickey), and flints from the Chalk : Quart. 

 Journ. Geol. Soc. vol. xv (1859) p. .41. See also Prestwich, ibid. vol. xxvii 

 (1371) p. 326, where he mentions a large fragment of red granite as occurring 

 at Trimley. 



