Rev. A. Irving— Water Supply from Bagshot Sands. 405 
Among the many schemes which have been advanced for the supply 
of London with water, it has been proposed by a high authority to 
bring the Bagshot Sands of the London Basin under requisition. 
These strata, covering, as they do, a considerable area at no great 
distance from the metropolis, and being for the most part of a 
porous character, would appear to form a convenient reservoir of 
water, since they contain stored up within them a large portion of 
the rain-water which falls on portions of Berkshire, Surrey, and 
Hants. The water obtained from these sands, either from surface- 
springs or deep wells, is free from calcareous hardness, but is highly 
charged with salts certain of iron, which, by oxidation on exposure 
to the air, yield an ochreous red precipitate, the nature of which 
seems generally to be but imperfectly understood. The incon- 
venience, however, which results, in the turbidity of the water after 
no great exposure to the air, and the rapid corrosion of iron pipes in 
which it is conveyed, are facts with which all inhabitants of the 
Bagshot country are only too familiar. The fact that this property 
of water drawn from the Bagshot Sands varies greatly according to 
the portions of those strata which furnish it, does not however 
appear to be so generally known. Recent difficulties in connection 
with the water-supply of our own particular district have forced the 
matter upon my attention ; and as I have been able to arrive at some 
pretty definite results from the investigations in which I have been 
engaged for several months past, it has occurred to me that, as 
forming a subsidiary subject to geological science, they may be of 
interest to readers of the Guorocroan Macazine. 
It was from Prof. Geikie’s Text-Book that I obtained the first 
clue, which has led me, I believe, to the true explanation of 
the green colour, which is so characteristic of a large portion of 
the sands of the Middle and Lower Bagshot series. The bearing 
of this upon the question of water-supply will appear as we 
proceed. My attention was specially drawn to this fact some 
months ago by the exposure of a section of light green sand (mixed 
with about 20 per cent. of fine clayey matter, which is easily 
separated from the sand itself by levigation in water), in the ex- 
cavation of a small lake-basin in this neighbourhood. The sand in 
question is an accumulation of mere surface-drift, little more than 
mere rain-wash, at the head of one of the minor valleys of erosion, 
which are so common in the Upper Bagshot Sands as to give a dis- 
tinct character to the country wherever these sandy strata constitute 
the higher parts of the terrain. These sands naturally are of a 
buff-yellow colour; and. the problem was to account for their 
greenness, when found in such a position as I have just described. 
The case mentioned is by no means a solitary one: the occurrence of 
these light green sand deposits has been observed by me in several 
instances, in similar positions, during the last few years, but from 
one cause and another the examination of them has been put off till 
quite recently. 
In a paper read during the early part of the summer before the 
Geologists’ Association i gave an account of the causes of this 
