Capt. Macdakin — Northampton Ironstone Beels. 
409 
distant from tlie Great Northern Railway, and overlooking the broad 
valley of Lias Clay, the top of the escarpment is forrned of the 
denuded edge of the Lincolnshire Limestone (Fig. 2 A). The 
borings near the edge show a thickness of the Lower Oolite, Lincoln- 
shire Limestone, of four feet, suddenly thickening to thix-ty feet or 
thirty-three feet, and maintaining this thickness to the eastward. 
The surface is almost entirely level for about a thousand yards from 
the edge of the escarpment, and then breaks into a succession of 
slight undulations (Fig. 5), until it is lost under the beds of Lower 
Oolite Clay or beneath the drift. 
From personal observation I believe these undulations to have 
been caused by the upper beds having slipped in the direction of their 
dip, over the Lias Clay, which retains the water that percolates 
through the Oolite beds and Northampton Sands. This folding of 
the strata may be seen to advantage in the railway cutting on the 
Grimsby line at Greetwell (Fig. 3), about a mile from Lincoln, 
with the Lower Estuarine Clay forced up here and there where the 
limestone has been fractm'ed. This escarpment is about a hundred 
and fifty feet in height, the whole being formed by the Lias Clay 
with the exception of the upper ten feet, which is Inferior Oolite. 
The top being scattered over with drift pebbles, which I have failed 
to detect in the Lias valley nearer than a mile and a half, when they 
again commence and form extensive gravel-pits at Boultham Moor. 
The Lower Estuarine series is next encountered, varying from 
eighteen inches to two feet, consisting of a very white sand and 
flaggy sandstone, and in sorne places of clay. 
Below this come the Northampton Ironstone beds (Fig. 2 C, and 
Fig. 1), having a very constant thickness of eight feet, and resting 
on the Upper Lias. The ironstone beds vary in richness and in 
their mineral characteristics : whilst the upper beds are siliceous, the 
lower beds are more argillaceous ; some of the richer bands contain as 
much as forty per cent. of iron, which in the more siliceous portions 
falls to twenty-eight per cent. The ore near the outcrop occurs in 
nodular masses on an average perhaps of a foot in diameter, sorne- 
times as geodes with concentric bands of oxidation, and occasionally 
containing a loose kemel of unoxidised blue carbonate of iron. For 
two hundred yards from the outcrop the beds are of a deep reddish 
brown colour owing to the silicate of iron ; then changing (Fig. 2 F) 
into the bluish grey carbonates (Fig. 1) • the red ore occasionally 
lining fissures plainly showing the cause of this change, from the 
original blue carbonate by oxidation to the brown clay ironstone 
nodules of the outcrop, which even still in some places exhibit on 
fracture a centre of the original blue carbonate of iron. Some por- 
tions of the peroxidised beds are very vesicular, the well-sinkers 
having from time immemorial called it “ Firestone,” believing it to 
have been the work of subterranean fires. 
Immediately over the Lias Clay there is a curious bed (Fig. 1, 
No. XI.), three inches in thickness, of phosphatic nodules, with 
pyrites, handsome brilliant masses, that the country people carry off 
as decorations for their chimney-pieces. A bed of micaceous clay 
