546 



On Chalk Marl 



the adjacent parts of Hampshire; that is/ from near Wreckles- 

 ham church, in the parish of Farnham, to Crondell church, in 

 Hampshire. 



The specimens, in every instance, were dug out of the true geo- 

 logical subsoil, three feet below the surface of the ground. The 

 lower members of the series crop out at no very considerable dis- 

 tance from each other — in some cases in the same field — while 

 the upper one, constituting the soft chalk with flints, lies nearly 

 parallel with the existing surface for many miles in a west-north- 

 west direction, in fact, throughout the extent of North Hants 

 into Wiltshire. 



So far as regards the external and agricultural characteristics 

 of the series of subsoils of which the chemical history is now 

 given, this section may be considered a fair type or representation 

 of the chalk of the South of England ; and we have observed, in 

 various localities in Hants, Surrey, Sussex, and Kent, that the 

 preference has always been given, for marling and chalking pur- 

 poses, to certain definite geological strata in the series, whenever 

 they were within reach of the farm, as the marl and chalk pits of 

 the older and present time abundantly testify. 



No. 1. The Lower Gault. — This, the lowest part of the gault, is 

 a blackish compact shaley clay. It rests upon the lower greensand^ 

 from which it is separated by a thin seam of phosphoric fossils 

 (described by us in vol. ix. of the Society's Journal), generally 

 accompanied by a thin band of impervious ironstone, which resists 

 the passage of water, thus rendering this portion of the gault 

 useless for agricultural purposes in its natural undrained state. 

 From this cause also the oak trees growing here are always 

 stunted in appearance ; but whenever, by natural or artificial 

 means, the obstruction from below is removed, this portion of the 

 gault clay immediately becomes susceptible of great fertility. 



As it always lies in close proximity to light sandy or gravelly 

 soils it has been often used, and practically found to be a valuable 

 alterative to such land, either directly by communicating its mi- 

 neral ingredients, or by furnishing an absorptive medium for the 

 retention of manure. 



The Analysis of the Lower Gault (No. 1), when dried at 212° Fahr., is as 



follows : — 



Per Cent. 



Combined water with a little organic matter . 7 "68 

 Soluble in dilute acids, 23*32 :— 



Silicic acid* (silica) 16*65 



* Those readers who are acquainted with analytical chemistry will understand that 

 the silica here stated to be soluble in acids is that which by treatment of the soil with 

 acids is rendered soluble in caustic potash or soda, which it would not be but for 

 such treatment. Its quantity indicates the extent to which the aluminous silicates 

 are decomposed by the action of mineral acids. 



