412 Rev. A. Irving— Water Supply from Bagshot Sands. 
Of the possible sources of nitrogen in peat and humus Julien! points 
out (1) the direct absorption of nitrogen from the atmosphere by 
humus during its oxidation, and of nitrous and nitric acids from 
atmospheric waters; (2) the exuviae and other remains of insects, 
crustaceans, worms, etc., which inhabit the swamps and morasses in 
which peat is formed; (8) the direct decomposition of the albuminoid 
substances found in plants. Each of these may well have played 
its part in the ancient swamps and morasses of Middle Hocene times, 
when these highly contaminated sands were deposited. 
It has been pointed out above that chemical analysis shows that 
the sands which are coloured with the deepest shade of green contain 
the greatest amount of vegetable pollution. This is further borne out 
by examination of these sands under the microscope. The green, 
dark-green, and black grains are the same in all the sands, but the 
colouring matter exists only as an incrustation upon the grains. 
I have not been able to find a single grain of any green mineral in any 
of them. In the sand of the darkest shade of green every grain 
contributes to the colour of the sand: the lighter shades of green 
in the other sands depend simply upon the proportion of the green 
and blackish-green grains to the sand as a whole. These grains 
are coated, in some instanees with colloid green matter, in others with 
a black opaque substance, the latter not spread uniformly over the 
surface of the grain, but adhering in numerous small particles to it. 
This is probably humic acid in combination with iron as a base. 
These materials form a tenacious glue, which not only adheres of 
itself to the larger grains, but cements smaller grains to them, 
giving them the appearance of a very rugged outline. For the 
most part decoction in caustic potash for several hours extracts the 
vegetal acids, so that when washed and dried the sand comes out as 
a very clean quartz-sand, the proportion of rounded grains to angular 
fragments (often of flint), varying very much in the different sands. 
Occasionally a hexagonal crystal of quartz, such as are to be seen 
often lining the hollows of flints, is met with, and in one instance 
two such crystals were seen attached to a rounded grain of amorphous 
silica.” As the cement is dissolved away in potash, the minute 
grains are detached from the larger ones, which in some specimens 
(those originally of the deepest green colour) come out as sharp 
clear angular fragments for the most part, while in other specimens, 
where more iron is present, that substance is found forming a thin 
film of peroxide on the surface of the grains, giving to the sand 
(originally of a dirty greenish tint) a light shade of red. The black 
colloid adherent matter of a few of the grains resists the action of 
the alkali for a long time, and these are seen, after decoction, still 
encrusted with it. Further chemical examination, details of which 
would take us beyond the scope of the present paper, has led me to 
regard this black material as humic acid in combination with iron 
and with silica, rather than as bituminous matter. Hnough has 
1 Ibid. p. 317, and the authorities there cited. 
> Of. J. A. Phillips Esq., on ‘‘ Grits and Sandstones,’’ in Quart. Journ. Geol. 
Soc. No. 145. . 
