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XVIII. — On the Silica Strata of the Lower Chalk. 

 By J. Thomas Way and J. M. Paine. 



The readers of this Journal will remember that in the Second 

 Part of the Twelfth Volume we published a paper on the Chemical 

 Composition of the Strata of the Chalk Formation — and that we 

 there gave a chemical and geological, as well as an agricultural, 

 description of the different distinctive beds from the gault clay 

 in an ascending series through the upper green sand and the 

 chalk marls to the upper chalk. 



The chemical investigation of these strata was undertaken from 

 the conviction which we entertained that a knowledge of the 

 composition of the various beds which in many cases come to 

 the surface and form the staple soil of large tracts of country, 

 and in others are but slightly covered with transported materials, 

 would be of the greatest possible advantage to the agriculture of 

 all those districts which are situated on the chalk formation : 

 and indeed we believe that the extension of this method to 

 the examination of other geological formations would be most 

 desirable. 



One of the beds or strata in the series referred to was de- 

 scribed under the name of soft brown rock " above the gault ; 

 and as it is of this bed and of those of the same kind that we 

 have now to speak, we shall make no apology for repeating the 

 analysis here. In page 549 of the above-mentioned paper we 

 find the description and analysis of the rock as follows : — 



" Immediately above the gault, with the upper member of which it in- 

 sensibly intermingles, lies this soft white-brown rock, having the appearance 

 of a rich limestone. It is very remarkable on account oi" its low specific gravity, 

 and still more so considering its position by reason of the very small quantity 

 of carbonate of lime which it contains. There are numerous small fissures in 

 the rock, which constitute a natural drainage. It is one of the richest subsoils 

 of the whole chalk series, being admirably adapted for the growth of hops, 

 wheat, beans, &c., and indeed nearly the whole of the out-cropping of this sub- 

 soil from Farnham to Petersfield is under cultivation for the first-named crop. 

 When exposed to frost the rock crumbles into a fine powder. In the neigh- 

 bourhood of Farnham, during the last ten years, many thousands of tons have 

 been dug and used as a manure, under the impression that it was a ' good 

 marl.' This is so far mistaken as regards the meaning of the word marl, which, 

 correctly speaking, should only be applied to a substance containing much 

 carbonate of lime. All those persons who have employed it concur in express- 

 ing a favourable opinion of its effects ; and particularly on some sandy soils 

 the benefit derived from its application is most striking. That we are not to 

 attribute this effect to the presence of lime in any form is evident from the 

 composition of the substance as given below. 



" At the present time it is still extensively quarried for manure. This section 

 of rock at Farnham is about 40 feet in thickness, and as it approaches the next 

 stratum above it gradually assumes a harder character, and does not so readily 

 moulder into soil by exposure. 



" Analysis of soft brown rock immediately above the gault : — 



VOL. XIV. Q 



