62 On the Phosphoric Strata of the Chalk Formation. 
Immediately below the soft marl-bed the first division of the 
green-sand formation commences, viz. the upper green-sand and 
firestcme rock. In its lithological and chemical character it is 
in reality a continuation of the superincumbent chalk strata, and 
has no connexion but in name (some parts of Devonshire perhaps 
excepted) with the lower green-sand. 
It commonly comprises three distinctive subdivisions. The first is a 
thin green band of marl, more or less silicious, abounding in organized 
fossil remains ; it lies below and is in contact with the soft dirty-white 
marl above mentioned ; in thickness it varies from a few inches to ten 
and fifteen feet. To this division the attention of agriculturists is par- 
ticularly invited, it being most remarkably rich in phosphate of lime. 
It rests upon a rubbly mass of broken-up rock, from 10 to 20 feet 
thick, which is also impregnated with a notable quantity of phosphatic 
matter. In this lower mass are nodules of a purely white substance (an 
analysis of which is afterwards inserted) thickly interspersed, which, with 
the peculiar green colour of the bed above them, may be serviceable as a 
means of identifying the stratum in different situations. 
The second subdivision is the firestone rock, or building stone. Its 
thickness is extremely uncertain; in some places consisting merely of 
one bed of stone, whilst in others it forms a series of layers, the aggre- 
gate thickness of which reaches to nearly 100 feet, as for example at the 
Undercliff of the Isle of Wight. This rock becomes softer in its lowest 
position, and gradually merges into a soft clayey marl, which constitutes 
the third subdivision. This again in its inferior parts becomes more 
and more argillaceous, until it is finally lost in the gault or blue marl 
stratum. 
The soil derived from the debris of the whole of the upper 
green-sand is notorious for the luxuriance of its crops, especially 
those of wheat and hops. In the counties of Kent, Surrey, and 
Hampshire it is in this particular geological formation that some 
of the richest plantations of hops flourish. 
The gault, which divides the upper from the lower green-sand, 
is most unmistakably recognised by its blue colour, almost merg- 
ing into black in its lowest parts, and also by its wet clayey texture. 
In its natural condition it is best adapted for pastures, and is 
celebrated for the growth of splendid oak timber ; but when this 
soil is deeply and thoroughly drained, it is capable of producing 
the heaviest crops of wheat, beans, clover, hops, &.c. The fossils 
in this stratum, though, as at present known, too few to be col- 
led ed for agricultural purposes, are invariably, amongst the speci- 
mens yet discovered, the richest in phosphate of lime. 
The lower green-sand in some districts is very largely deve- 
loped, containing within its limits soils possessing every grade of 
natural fertility — from the poor arenaceous heathlands of Surrey 
to the rich ragstone rock in the neighbourhood of Maidstone. It 
is remarkable in one of its characteristics, as well as interesting 
