226 



On the Silica Strata of the Lower Chalk. 



Per cent. 



Combined water and a little organic matter . . 4*15 



Soluble in dilute acids, 57* 10 : — 



Silicic acid (silica) 46 •2S 



Carbonic acid ...... none 



Sulphuric acid ...... trace 



Phosphoric acid ...... ditto 



Chlorine ....... none 



Lime ....... 0*26 



Magnesia , . . . . . . '07 



Potash -79 



Soda '43 



Protoxide and Peroxide of iron . . . 6*12 

 Alumina • . . . , . .3*15 



Insoluble in acids, 38*75 : — 



Lime 2'91 



Magnesia ....... traces 



Potash 1-51 



Soda '60 



Alumina, with a little oxide of iron . . 14*20 

 Silicic acid and sand . . . , .19*53 



100-00 



And at tlie end of tlie paper it is remarked that a further careful 

 study of this rock may throw light on the composition of soils. 



We were not unaware at that time of what we have since learnt 

 more fully, that this particular stratum of earth contained a large 

 proportion of silica in that peculiar form or condition which is 

 known to chemists under the name of soluble silica ; but we were 

 unwilling to mention this circumstance until, by careful investi- 

 gation, we had assured ourselves that the substance in question 

 existed in quantity and under conditions that would render it 

 available for any agricultural use to which its peculiar properties 

 might adapt it : in fact, we desired to ascertain, before inviting 

 attention to the subject, that this soluble silica rock might serve 

 some more useful purpose than to be placed as a curiosity 

 in the cabinet of a geological collector. Since the publication of 

 that report upwards of one hundred specimens of the earth have 

 been collected at different depths and from different spots where 

 the stratum is found (in the neighbourhood of Farnham), and 

 have been transmitted to London for analysis ; and it is the object 

 of the present paper to record these examinations, and to describe 

 the stratum generally, as well as to point out, so far as they have 

 occurred to us, the uses to which this source of soluble silica 

 may eventually be applied in the interests of agriculture. 



But, before we proceed further, it will be necessary to explain 

 what is meant by soluble silica. The most common forms of 

 silica known to the farmer are those of sand, flint, and pebbles, 

 and as such, silica constitutes a very considerable portion of 

 the crust of the globe ; but by far the largest quantities of this 



