406 Rev. A. Irving—Water Supply from Bagshot Sands. 
peculiar greenness of sands occurring in such a position, together 
with the outline of the evidence which had been obtained, which 
goes to show that the green colour of these sands is due to 
decomposed vegetable matter. In these wild uncultivated tracts, given 
up to the growth of pine-woods, heather, heaths, ferns, and marsh- 
plants, the natural drainage is often impeded in those small valleys 
which I have described by a dense mass of rank vegetation, which 
has been growing there for ages. In many cases peat has formed 
in such spots, sometimes as much as three or four feet in thickness ; 
and in every instance in which I have observed it, this green colour 
of the surface sands occurs below such peaty deposits. Further, 
this green colour is not destroyed by the action of either hydro- 
chloric or nitric acid; so that it cannot be referred to any of the 
varieties of green minerals which may be included under such terms 
as viridite, glauconite, delessite, etc. Slow oxidation reduces the 
green colour to some extent, as is seen in the effect of the air upon 
the colour of the sands when they have been spread out upon the 
surface of the ground for several months; and a similar effect has 
been produced by drawing air through a small quantity of the sand 
suspended in water for five or six days and nights continuously. 
The colour also is partly removed by a powerful oxidizing agent, 
such as chlorate of potash dissolved in the strongest red fuming 
nitric acid. The colour is at once destroyed by boiling concentrated 
sulphuric acid, which, while it entirely removes the green colour, is 
itself blackened, in some instances becoming as black as ink, by the 
separation in the elementary state of amorphous carbon from the 
organic compounds to which the green colour is due. It was at 
this point that the remarks which are ‘to be met with in Professor 
Geikie’s book on the part played by humic, crenic, and apocrenic 
acids (products of vegetable decomposition), were found of service. 
The only information I have been able to obtain in the scientific 
literature of this country, on the nature of these organic acids, is 
found in Watts’ Dictionary of Chemistry; but thanks to the kindness 
and courtesy of Professor Williamson of University College, who has 
furnished me with a copious list of references, I have been able to 
learn more about them from foreign sources, and in particular from 
that mine of information, Berzelius’ Jahresbericht. Doubts have 
been expressed in some quarters as to the existence of these acids ; 
but a perusal of the information given by Berzelius and others 
leaves no doubt in my own mind of their existence as veritable 
organic acids. Their actual chemical formule may not have been 
determined with any degree of certainty; but they form with bases 
well-recognized salts, the most important being those of iron and 
the alkali metals. Crenic salts are far more soluble in water 
than apocrenic salts, and as the former pass into the latter to 
a great extent by oxidation, and the basic iron becomes more 
highly oxidized, there remains no longer any difficulty in explain- 
ing why water charged with them in solution throws down a red 
ochreous precipitate of iron salts, on mere exposure to the air. Such 
a precipitate, when boiled in a solution of caustic potash or soda 
