On the Silica Strata of the Lower Ckalh. 



233 



point through the firestone, rubbly rock, and phosphatic green 

 marl, to the " grey marl " above, there is a gradual declension of 

 soluble silica as the analyses will indicate. 



The above facts were ascertained by cutting two trenches 

 respectively about 200 and 400 yards Ions: down to the true geo- 

 logical subsoil in two fields in Dippen Hall and Deans farms, 

 about half a mile apart. These two sections give similar indica- 

 tions and were corroborated by the marl pit in Crondall-lane, 

 about three quarters of a mile from the nearest of the other 

 sections. 



In these sections the dip to the north-west is about 20 

 degrees, and the valley being denuded in the opposite direc- 

 tion gave us a good opportunity of obtaining accurate results. 

 The samples were taken w^henever a change in the aspect of the 

 subsoil was remarked. In only one instance below the firestone 

 did we find a layer containing carbonate of lime ; this was about 

 4 feet thick (Xo. 31 in Section II.). We have, however, subse- 

 quently noticed a similar layer at Selbome. 



I. — SourH-'^i\'EST Sectiox, at FamharQ. 



From Deans Bottom and Hanger, in"" Deans Farm," over a surface of about 3S0 

 yards, from south-east to nortli-west. 



No. 



Silica. 



Carhonate 

 of Lime. 



Remarks. 



13 



2 



34 







Near the gault, approaching a clay in appearance. 



75 



16 



03 







Soft rock which readily crumbles into dust. 



42 



27 



81 







Eather harder. 



12 



37 



01 







Slightly harder, though still a crumbling rock.' 



90 



58 



88 







Hard, but veiy light and porous. 



41 



41 



73 







Softer rock, like 12 in texture. 



40 



43 



73 







About as 41. 



37 



40 



56 







Ditto- 



36 



47 



55 







!More compact, rather hard. 



19 



58 



67 







Hard like 22. 



' 71 



72 



66 

 43 



75 

 94 







Hard and rather cherty looking. 



Verv soft stratum, like marl, 4 feet thick, lying between 

 71 and 73. 



73 



58 



45 







Hard layer of rock below 72. 



39 



72' 



00 







Hard, compact, light rock, 10 feet thick. 



78 



58 



52 







Brittle rubbly rock below 39. 



37 



40 



56 







Softer. 



36 



47 



55 







About as 37. 



77 



8 



20 



74 



96 



Blue building limestone. 



76 



56 



62 







White building-stone, or "firestone," 20 feet thick. 



48 



40 



75 



20 



86 



Eotten stone above 76. 



49 



13 



26 



62 



22 



Thin flaky stone, lying above 48. 





29 



14 







Green marl. 





1 



82 



65 



52 



The grey marl " referred to in the text above, which 

 terminates the series. 



In the above section we consider the vertical depth of the rock, from Xos. 42 to 

 48 inclusive, to be upwards of 100 feet. 



