140 Mr Rastall, The Mineral Composition of 
The exact stratigraphical position of this gravel is uncertain : 
it is situated near the margin of a low plateau, which slopes down 
somewhat suddenly within a short distance to the alluvial flats 
of the Great Ouse. In general appearance it strongly resembles 
the gravels of the Cam, and it is included here for the sake of 
comparison. 
V. Surface Deposits. 
Blown Sand, Lakenheath Warren. 
This specimen, which was collected by Dr Marr as an example 
of the superficial wind-transported deposits of the Brandon district, 
consists of a very clean sand, remarkably free from muddy material, 
but containing a good deal of black fibrous vegetable matter. The 
effervescence with acid was very slight and the sample required 
very little preparation. It gave a fairly large dark residue in 
bromoform, and as most of this was obviously ferruginous it was 
at once treated with acid and allowed to stand for some time, 
washed and re-separated. The final product was small in amount 
and the constituent grains were of very small size as compared 
with those of the sands presumably laid down in water. The only 
mineral occurring in fairly large grains is garnet, which is also 
rather angular; all the other constituents are very round (except 
staurolite, which appears to remain angular under all circum- 
stances). 
The minerals identified are garnet, tourmaline (sometimes 
blue), kyanite, staurolite, hornblende, augite, hypersthene, epidote 
and rutile. Zircon is much more abundant than m any other 
specimen here described. 
Surface Deposit, Fowlmere, near Thetford. 
This is a sandy deposit, of a curious grey colour when fresh ; 
the peculiar colour is probably due to the absence of the usual 
iron oxide. When washed and treated with dilute acid it is 
found to consist principally of clean white quartz sand, with a 
few reddish grains. 
The minerals of the heavy residue are much as usual, namely, 
magnetite, garnet, tourmaline, hornblende, augite, epidote, zoisite, 
kyanite, staurolite and zircon. The staurolite is as usual angular, 
but the other minerals are well rounded, and this is specially 
notable in the garnet, which shows signs of more attrition than 
in any other sample examined. This may safely be attributed 
to wind action. 
The particles show a wide variation in size, but the majority 
are small. | 
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