On the Silica Strata of the Lower Chalk. 237 



whether of corn or turnips. Gypsum, too, upon seeds is a manure 

 always used with great success upon the soils of the malm rock ; 

 while upon those of the gault it produces no effect whatever. The 

 latter result we should have anticipated, as our investigations 

 have led us to discover an abundance of crystallized sulphate 

 of lime in the gault clays. 



From the foregoing description it will, we hope, be gathered 

 that, in certain parts of the country, and especially in parts of 

 Surrey and Hampshire, there occur at the base of the chalk 

 formation, and immediately above the gault clay, large deposits 

 of silica in the soluble condition. The silica is mixed with ordi- 

 nary clay in different proportions, and with these two ingredients 

 a third, carbonate of lime, is associated in some of the beds. 

 The percentage of silica varies from 5 per cent, up to about 70, 

 or somewhat more. Of this highest percentage a large quantity 

 could with ease be obtained, but we may safely assert that it 

 would be practicable to quarry many hundreds of thousands of 

 tons, containing as much as 60 per cent. Twenty or thirty 

 tons were sent to London for the purpose of being made into 

 manure, and upon being ground up the bulk was found to average 

 64 per cent, of soluble silica. 



We believe then — and, having taken very active and effectual 

 measures to settle this point, we are justified in believing — that, 

 for any purpose, agricultural or manufacturing, any quantity of 

 this earth that could by possibility be required could be supplied 

 from Famham and its neighbourhood. 



It becomes us next to inquire in what way a supply of soluble 

 silica can benefit, or be made to benefit, practical agriculture. 



The direct use of alkaline silicates as manure has not hitherto 

 been extensively tried in this or other countries. What little 

 experience of the effect of silicate of potash or soda we do pos- 

 sess is not remarkably favourable to their employment. Still 

 the difQculty of manufacturing the alkaline silicates in a proper 

 form, and the great expense of these salts, has quite precluded a 

 fair trial of their merits as manure. We do not think, then, that 

 the question of the use of soluble silicates as manures for cereal 

 crops is by any means settled. 



The discovery of this bed of soluble silica offers facilities for 

 the production of silicates of soda and potash, of which the ma- 

 nufacturer of these salts will assuredly not be slow to take advan- 

 tage. It is another and an ulterior question whether, when, by 

 moderate price and proper form for application, they are brought 

 within his reach, the farmer can make an advantageous use of 

 them. 



We will, however, shortly state what facilities we consider 

 these beds to furnish for manufacturing silicates. The great 



