24 



ME. G. M. DAYIES 01* THE 



[vol. lxxv r 



ferruginous sandstone. It is uniformly fine in grain and somewhat 

 loamy, as the following table shows : — 



Sand on Sand through 

 90-mesh 90-mesh 

 sieve. sieve. 



per cent. per cent. 

 Nearly white sand, main workings. 0*4 79*2 



BnfP sand, do. 0-4 84'4 



Buff sand, Nore Hill 1-7 69-0 



< , ' 



Yellow sand, main workings ' 74*0 



Red sand, do. 79'6 



Red sandstone, do. 58*8 



* Mud and iron-oxide. 





Diameter 





of 



Mud. 



largest 





grain. 



er cent. 



mm. 



20-4 



1-8 



15*2 



1-3 



29-3 



1-4 



26'0 



0-9 



20-4 





41-2* 



1-1 



The sand consists mainly of quartz, with some flint and white 

 mica. Felspar is very scarce, though plagioclase and microcline 

 have been seen. No glauconite was observed. 



The heavy residue ranges from 010 per cent, in the nearly 

 white sand to 0*22 per cent., with an average of 0\15. The variation 

 is mainly due to the presence of ferruginous matter. Apart from 

 this and white opaque grains, the chief heavy minerals are zircon, 

 ilmenite, rutile, kyanite, tourmaline, and staurolite. Small amounts 

 of magnetite and yellow and blue anatase are generally present, 

 and in some cases a few grains of andalusite, brookite, epidote, 

 green spinel, and possibly monazite were seen. 



Most of the minerals named occur throughout the Lower London 

 Tertiaries of Surrey and Kent. Anatase, it is true, is unusually 

 plentiful, and brookite, which is a decidedly rare mineral in these 

 counties, was noticed several times ; but such sporadic occurrences 

 are of no stratigraphical significance. Garnet, which was not 

 observed in these sands, is usually present in the Thanet Sand, but 

 often absent in the higher beds. The absence of glauconite, too, 

 would be exceptional in the Thanet Sand and in the lower part of the 

 Reading Beds, while it is the usual condition in the Blackheath Beds. 

 The supposed Pliocene sands and pebble-beds, which occup} r similar 

 positions at Headley Heath and elsewhere on the Chalk of Surrey, 

 are coarser and carry less flint, more mica, and striking amounts 

 of monazite and andalusite. In mineral composition, therefore, 

 the sand has more affinity with the Blackheath Beds or some of the 

 Reading Beds than with any other formation, and the association 

 with thick masses of pebbles suggests Blackheath Beds rather 

 than Reading. While these deposits were accumulating on the 

 flank of the London Basin, however, it is possible that anything- 

 from Thanet Sand to London Clay may have been forming in the 

 deeper and more central part of the basin. 



