﻿Capt. MacdaMn — Northampton Ironstone Beds. 409 



distant from tlie Great Northern Kailway, and overlooking the broad 

 valley of Lias Clay, the top of the escarpment is formed 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 thirty 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 fractured. 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 some 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, some- 

 times as geodes with concentric bands of oxidation, and occasionally 

 containing a loose kernel 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 



