Vol. 50.] 



fLEISTOCENE DEPOSITS AT TWICKENHAM. 



457 



might be due to free carbon, a sample of it was submitted to 

 Mr. William Chattaway, F.I.C., along with one from the lighter- 

 coloured sand above, to see if any further light could be thrown 

 upon it by the chemist. The subjoined analyses, together with 

 Mr. Chattaway's remarks which accompanied them, showed that 

 there was every reason for continuing our search for organic re- 



A. 



Reddish-yellow 



Sand from above 



Dark Loam Layer, 



Pope's Grove, 



Nov. 1st, 1892. 



Moisture 



Combined water 



Organic matter 



Silica 



Ferric oxide , 



Alumina 



Lime 



Magnesia 



Soda and potash , 



Carbon dioxide (combined) 



Sulphuric anhydride 



Chlorine 



•21 per cent, 

 trace. 



•04 „ 



94-40 „ 



L76 „ 



273 „ 



•23 „ 



•16 „ 

 trace. 



•19 „ 



•26 „ 

 trace. 



99-98 per cent. 



B. 



Dark Loam Layer, 

 Pope's Grove, 

 Nov. 1st, 1892. 



11-68 percent. 



•31 „ „ 



2-36 „ „ 



65-11 „ „ 



1*28 ,, „ 



2-66 „ „ 



8-78 „ „ 



•40 „ „ 



trace. 



7-03 „ „ 



/33 „ „ 



distinct trace. 



99-94 per cent. 



The following observations accompanied the analyses : — 



(1) The lime is probably wholly present as carbonate in sample 

 B ; but in sample A it may probably be present as sulphate. 



(2) The organic matter in B is largely carbonaceous, but Mr. 

 Chattaway has not fully satisfied himself of its nature. 



(3) There is probably only magnesium carbonate in the case of 

 A, for, singularly enough, the amount of carbon dioxide found will 

 exactly combine with the magnesia. That base is probably also com- 

 bined with C0 2 in B. 



(4) By ' combined water ' is meant that which is not lost at a 

 temperature of 100° C, but is held chemically, or else in some mole- 

 cular way. This was of course determined by heating the sand to 

 redness, and collecting the water in a tube packed with calcium 

 chloride. 



Later on we were abundantly rewarded by finding numerous 

 shells, seeds, and much vegetable debris. 



Extensive washings were made of the loam by Mr. H. M Bennett, 

 and they were submitted to Mr. Clement Beid, F.L.S., F.G.S., who 

 kindlv determined them for us as follows : — 



