135 



NOTES ON A MANGANIFEROUS SEAM IN THE 

 THAMES VALLEY DRIFT AT ILFORD, 

 ESSEX. 



By J. P. JOHNSON. 



The continued erection of houses on the site of the old 

 Uphall Brickyard has necessitated the opening of several new 

 pits for the supply of building material, since those described in 

 an earlier paper' were filled in. As a rule the sections thus 

 exposed shew no additional features of interest and further back 

 attraction in that they have not yielded any fossils.^ 



However, there are exceptions to every rule and the follow- 

 ing section which is situated between the " Hunter," " Uphall " 

 and " Harvey Eoads," is well worth noting : — 



Fine Ochreous Gravel . . 4 ft. 



Ochreous Sand . . . . 3 ft. 



White Sand . . . . i ft 



For between the gravel and sand, which pass into one 

 another, there is a lenticular seam coloured black with hydrated 

 oxide of manganese, which occurs in the amorphous form of 

 psilomelane, coating the grains and pebbles 



I took three samples from different parts of the seam with 

 the object of determining the percentage of manganese present. 

 Sample i. was estimated by my friend, Mr. \V. G. Rumbold, to 

 contain 27 per cent. Sample ii., which was kindly analysed 

 by my friend Prof. Geo. Patchin, A.R.S.M., and by Mr. F. A. 

 Zurcher, yielded -975 per cent., while sample iii., which was 

 assayed by myself, contained only -68 per cent. All three 

 samples were assayed gravimetrically by the "basic acetate" 

 process, and very carefully checked by duplicate assays. 



It will be seen that the results vary somewhat, but their 

 difference is not greater than might have been expected from the 

 nature of the deposit, because, since the psilomelane occurred 

 only as a film on the exterior of the pebbles and grains, the 

 sandy portions of the seam would naturally contain more 

 manganese than the pebbly portion. 



1 J. P.Johnson, ' Additions to tlu Palasolithic Fauna of the Uphall Brickyard, Dford." 

 Essex Naturalist, vol. xi. figoo), pp. 209-215. 



2 I have, however, obtained the greater part of a large hache which I have handed over 

 to the lissex Field Club's Museum at Stratford. It is very much abraded and is probably 

 derived from the high-level drift of this valley. 



