242 



On the Silica Strata of the Lower Chalk. 



to plants, and that in good loamy soils they are modified and 

 changed into slightly soluble silicates, it will evidently be an 

 approach to this condition, if in light soils we can induce the 

 conversion of the different salts of ammonia into the form of 

 silicate of ammonia, which is believed to be the actual form in 

 which in good soils it is presented to the roots. 



The simple silicate of lime of which we are now speaking 

 must not be confounded with the compound form — silicate of lime 

 and alumina : this latter actually, as we have before seen, sepa- 

 rates and renders insoluble the ammonia of manure ; silicate of 

 lime will not do this, and it cannot be looked to as a means of 

 making light land more retentive of manure ; but if, as we hope, 

 it should be found to render the use of nitrogenous manures, such 

 as guano, &c., more safe on light land, and should facilitate the 

 growth of large crops on such lands by the use of abundance of 

 manure, a great advantage would be obtained for the agriculture 

 of this country. We think, therefore, that silicate of lime is 

 well worth trying as a means of brightening and strengthening 

 the straw of cereal crops on light land, and of checking the over 

 luxuriance due to high manuring. It might be made very 

 cheaply — probably at a cost of less than 3/. per ton — and from 

 2 to 3 cwt. would be a sufficient application per acre. It might 

 be applied either in the autumn or as a top-dressing in early 

 spring ; but, from its comparative insolubility, it would be better 

 to have it well diffused through the soil, and therefore the autumn 

 would probably be the best time for applying it.* 



We have already mentioned the advantage obtained by the 

 application of lime on those lands where this rock shows itself 

 near the surface : for the districts where it is easily obtained it 

 may be often desirable to apply the silica marl with lime, either 

 separately or at the same time, trusting to the combination taking 

 place in the soil. Where lime-kilns exist in these districts, a very 

 easy method of forming the silicate would be to heat gently the 

 building-stones (Nos. 54, 60, 76, 77) which we have described 

 as containing carbonate of lime mixed with soluble silica. The 

 burning will be effected in the same way as that of common 

 chalk, but at a lower temperature. 



The discovery of these silica beds brings us a great way nearer 



* On the 12th April in this year, upon some wheat grown on a gravelly soil, 

 resting upon the lower greensand, naturally poor but well cultivated, and manured 

 with dried blood at the rate of 5 cwt. per acre, was applied on 10 perches 28 lbs. of 

 the double silicate of alumina and ammonia ; two perches were then missed, and on 

 another 10 perches" 60 lbs. of silicate of lime was applied ; two perches were again 

 missed, and on a third plot of 6 perches 39 lbs, of silicate of soda was applied. 

 At this time (8th June) all the three plots are manifestly better than the unsilicated 

 portions, the straw being from 4 to 6 inches higher, and not quite so dark a colour. 

 — J. M. Paine. 



