376 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [ Mar. 9, 
material,—by infiltration doubtless; but whence derived, is a pro- 
blem yet, I think, to be solved. 
The beds have thus undergone change—-have been doubly meta- 
morphosed,—first in the introduction of the iron, and secondly in 
the altered form in which the iron is now exhibited in the cellular 
ironstone. 
There can be little doubt that at some period the iron, subject to 
local variations as to proportion, was equably diffused thronugh- 
out the mass of impregnated material (even as now it is in the 
slightly ferruginous brown sandstones of the Northampton beds): 
it afterwards, in obedience to some subtle principle yet to be deter- 
mined, separated from the associated material, and arranged itself 
as walls of cells, ever varying in form (some being rectangular, 
many irregular and many-sided and often with rounded angles, some 
nearly spherical, and occasionally concentric), but all containing 
cores of the original material—whether sand, marl, or clay—from 
the majority of which the iron has almost entirely departed. 
The quantity of iron present in these beds offers also a fertile 
subject for consideration. The ore yields on an average 40 per cent. 
of pig-iron—sometimes more than 55 per cent. From this Duston 
pit alone, more than 1000 tons of ore per week are sent away ; 
and the weekly produce from the county of Northampton is from 
9000 to 10,000 tons, yielding from 3000 to 4000 tons of pig-iron. 
This has been going on for some ten or twelve years, certainly not 
always at the same rate as now; but were we to dot out on the 
map the comparatively few excavations from which already such an 
immense amount of iron has been obtained (say a million and a half 
of tons), and compare the area of these with the whole area occu- 
pied by the ferruginous beds of the county, we should arrive at 
such an idea of the aggregate quantity of iron imported into these 
beds subsequently to their deposition, as to involve in considerable 
difficulty the question of its derivation and of the conditions under 
which it was introduced. 
South of Duston is the east and west branch of the valley of the 
Nen, and immediately south of Northampton is the conflux of this 
branch with the northern branch of the same valley. About two 
miles west of this point commence thick alluvial beds, which oec- 
cupy, with a bordering of Upper Lias Clay, the Nen valley and its 
tributaries for many miles to the east and north-east. The upper 
bed here consists of an earthy clay with much vegetable matter ; 
and in its lower portion it is spotted bright blue by nodules of 
Vivianite or phosphate of iron: it contains at its base numerous 
remains of ox, deer, horse, and wild boar, frequently stained blue 
by the same mineral. The lower bed consists of a sandy gravel, 
from which I have obtained teeth of Hlephas antiquus and primi- 
genius, bones of Hippopotamus, and teeth both of the upper and 
lower jaws of Rhinoceros tichorhinus. This alluvium overlies the 
Upper Lias clay. 
On the southern side of the valley is Huntsbury Hill, a projecting 
