Chi the Agricultural Geology of the Weald. 247 
state* varies from 2 to 75 per cent. "Those beds which contain 
a high percentage of silica are, when dry, remarkably light, of a 
fawn or reddish yellow colour, and very soft, except in some 
instances where the silica is associated with carbonate of lime. . ," 
The persistency of this soluble silica over large areas upon 
the same geological horizon is very remarkable. Messrs. Way 
and Paine examined the Upper Greensand of the Isle of Wight, 
and there found soluble silica, though to a less extent than at 
Farnham. They quote an analysis, by M. Sauvage, of the Upper 
Greensand at Ardennes, where the bed contains 56 per cent. An 
analysis recently published of the same bed, in the Pays de Bray, 
gives 50 per cent, of soluble silica.t 
The outcropping of this stratum is everywhere characterised, 
by great fertility, and is especially remarkable for the excellence 
of its wheat and hops. Large quantities of the siliceous rock 
have been dug as manure.' 
The terrace formed by the Upper Greensand is particularly 
well marked in Hants and West Sussex. 
Besides the papers by Messrs. Way and Paine, this district 
has been described in the ' Report on Surrey,' by Mr. H. Ever- 
shed,! in that on Hants by the Rev. T. Wilkinson.§ It is 
therefore unnecessary to go again over ground which is already 
familiar to readers of this Journal. 
The Gault. 
This division exhibits less variety in its character than any 
other, excepting perhaps the Chalk. I*" consists everywhere of a 
blue or black clay, which weathers brown, and is occasionally dug 
for tiles. Its soil, known as " black land," is always stiff and hard 
to plough, but when drained it makes excellent land ; perhaps 
as good as any in the South of England, except the Upper 
Greensand. At present a large proportion of it is in pasture. 
The middle portion is most productive ; it contains the greatest 
percentage of carbonate of lime, and is, in fact, a marl. 
At the base, and resting immediately on the Lower Greensand, 
is a phosphatic layer, which is remarkably persistent throughout 
of the Chalk Formation,' vol. ix., p. 5G ; and 'The Chemical and Agricultural 
Characters of the Chalk Formation,' vol. xii., p. 544.) These three papers, taken 
together, are certainly the ablest contribution to Agricultural and Chemical 
Geology that have appeared in England. 
* That is, soluble only very slightly in water, but largely so in alkaline solu- 
tions. 
+ Lapparent. ' Bull. Soc. Ge'ol. de France,' ser. 2, torn, xxiv., p. 230. 
X ' Journal of the Eoyal Agricultural Society,' vol. xiv., p. 406. 
§ Ibid., vol. xxii., p. 254. An excellent description of the Chalk area of Hants 
(applying also to that of West Sussex) is given in this report. 
