limestone are exposed. At the Apethorpe "town-pit " beds of light-blue clay and marl appear in the same position. Upon the side of the hill, on the right bank of the Willow Brook, and opposite to the village of Kings Cliffe, a pit shows the limestone with hard, quartzose, laminated beds exhibiting mammillated surfaces at its base, and resting on the white sands with carbonaceous markings and plant remains. At Yarwell, on the west bank of the Nene, the Northampton Sand is evidently thin; it is composed principally of white sand, and its junction with the limestone above and the clays below was seen. On the opposite side of the river, at New Close Cover, the Lower Estuarine beds are dug in a small pit, affording the following section : (1.) Soil. (2.) Brownish-yellow sand (3.) Black band, entirely made up of car- 3 inches. North of Stibbington the ferruginous sands can be traced at the fish-ponds, and the white sands have been found underlying the oolitic limestone in the great pits south of Wansford. The same beds are seen underlying the Lincolnshire Oolite in the cutting between Wansford station and the Wansford or Sibson tunnel, and here, as will be afterwards shown, we have a complete series of the Great and Inferior Oolite beds exposed. At Water Newton brickyard the sands and clays of the Lower Estuarine series are dug under the beds of oolitic limestone which are here only of insignificant thickness. Along the small tributary valleys in which are situated Southorpe, Thornhaugh, Wittering, &c., the sands and ironstones of the lower part of the Inferior Oolite can be traced, but they appear to be generally very thin and afford no good sections. Along the valley of the Nene eastward, the beds in question are almost always concealed by the thick deposits of valley-gravel. At Milton Park and at Peterborough, wells have been sunk, which passed from the Upper Estuarine clays directly into white sands of the Lower Estuarine, the Lincolnshire Oolite having entirely thinned out. Inliers. The great plateau formed by the Lower Oolite beds is frequently cut through by the numerous streams which intersect it, so as to expose in the sides of narrow valleys all the strata down to the Upper Lias Clay. This exposure of the lowest beds of the Inferior Oolite is frequently aided by the numerous faults which intersect the district, and throw the beds in question to much higher levels than those which we might anticipate they would occupy, from their general dip. In the inlier at Pipwell, which is cut down to the Upper Lias Clay in its western part, through an upthrow of the beds, we find a number of exposures of the Northampton Sand. Near Pipwell Upper Lodge the ironstone beds are dug in a small pit ; and halfa-mile westward traces of an old reservoir are seen in the valley, at a point where abundant springs issue at the junction of the ironstone with the Upper Lias Clay. The Northampton Sand is also well exposed in the deep gorges near the junction of the two small streams above Pipwell Abbey. At the inlier at Corby and Weldon there are many exposures of the Northampton Sand, the succession of the beds exhibited at a number of different points in road-cuttings, &c. being: (1.) Lincolnshire Oolite Limestone, becoming sandy at its base and sometimes exhibiting traces of fissile stone (Collyweston Slate). (2.) Very variable beds of sand and clay with numerous plant remains. (Lower Estuarine Series.) (3.) Ironstone beds, with usual characters. (4.) Upper Lias Clay. The Northampton Sand here exhibits the usual very great variation in thickness and mineral characters. Between Corby and Little Weldon the same succession of beds is seen at several points; near the latter place they suddenly disappear, the limestone being let down against them by a fault. The manner in which a rock of the impure shelly and oolitic limestone of the Northampton Sand passes, often within very short distances, into beds of white sand or ironstone is very strikingly exemplified in this neighbourhood. In many places the limestones are themselves very ferruginous and exhibit the peculiar banding with thin seams of brown hæmatite, developed along lines parallel to those of bedding and jointing, which is so striking a feature in the Northampton Sand. Precisely similar phenomena are exhibited in Yorkshire in the country south and west of Malton, where the great estuarine series of the Lower Oolites, which form the north-east moorlands of Yorkshire are greatly reduced in thickness, while in their midst there are developed a number of, sometimes locally important but always extremely inconstant beds of more or less sandy oolitic and shelly limestone, precisely agreeing in character with those of the Northampton Sand. The presence of these inconstant calcareous rocks appears to be very characteristic of series of strata, exhibiting other evidences of the alternations of freshwater and marine conditions at the period of their deposition. The small valley at Brigstock Parks exhibits the Inferior Oolite limestones and sands considerably disturbed, and as already explained, unconformably overlaid by the series of Great Oolite beds. Between Sudborough Lodge and the Brigstock Park Lodges we find a pit opened in the summit of a small anticlinal in the ironstone beds of the Northampton Sand. About Little Oakley and Stanion the valley, cut through the Boulder Clay and Great Oolite beds by Harper's Brook, exposes the Inferior Oolite strata along its sides similarly faulted and rolled, and unconformably overlaid by the Great Oolite series. The ironstone beds at the base of the Northampton Sand have frequently been dug in the wells and cisterns at the village of Stanion; while about Little Oakley there are numerous exposures of the white sands and clays of the upper part of the series, and the ferruginous rock of its lower part; they offer, however, no special features of interest at this place, and will be noticed in connexion with the beds of the Lincolnshire Limestone in this inlier. At Brigstock Mill, an interesting section in the brickyard and wells, to be hereafter fully described, exhibits the whole of the Lower Oolite series from the Upper Estuarine series down to the Upper Lias, this place being near the line of the easterly disappearance of the Lincolnshire limestone by attenuation. The succession of the Northampton Sand beds at this place is given on page 191. A long narrow inlier of the Northampton Sand is seen in the upper part of the valley of the Willow Brook, near Dene, Bulwick, and Blatherwycke, but there are seldom good exposures of the strata. At Dene brickyard we have the following section : (1.) Marly limestone (2.) Whitish, calcareous sands (3.) Hard, blue-hearted, sub-crystalline limestone - 1 to 2 feet. 1 foot 6 inches. 1 foot 6 inches. 2 feet. (11.) Sandy ironstone (dug in a well) 3 feet. 1 foot. 6 to 8 feet. 6 feet. 1 foot. 3 feet. 3 to 4 feet. I regard all the beds from (7) to (11) inclusive as belonging to the Northampton Sand. This section is of great interest as presenting another type of the Northampton Sand, namely that in which a great part of the formation is represented by beds of dark-coloured clay. These beds have in some instances been mistaken for the Upper Lias, and have, indeed, been sometimes mapped as such. A close inspection, however, soon convinces the observer that the resemblance is a very superficial one, and is confined almost entirely to colour. The clays in question are totally wanting in the tenaceous character of the Upper Lias, and indeed they are composed quite as largely of arenaceous as of argillaceous materials; their dark colour appears to be due to the large quantity of organic (vegetable) matter which they contain. At Blatherwycke Park similar beds to those at Dene brickyard have been penetrated in several wells. About 30 years ago a well at the top of the hill sunk to the depth of 60 feet (?) appears to have reached, at the level of the ornamental water in the park, a spring, the water of which is said to have been strongly impregnated with sulphuretted-hydrogen, and to have acted as a powerful purgative. Another well sunk into the rock of the Northampton Sand was the means of obtaining a very copious supply of water. In the valley known as "Hollow Bottom," the freshwater sandy clays of the Lower Estuarine Series are exposed in the brook to the south of Bulwick Woods. Higher up the brook the ironstone beds can be traced, and the very numerous fragments of slag seen on the ploughed fields indicate that the smelting of the ore was carried on at this spot at some former period. The various beds of the Northampton Sand were also traced, though somewhat obscurely, at the bottom of the little valley at Tryon's Lodge, where they form a very small inlier in the midst of the great spread of Lincolnshire limestone. The clays of the "Lower Estuarine Series can in like manner be traced in the valley in which Fineshade Abbey is situated. In consequence of the great north and south fault of Ketton and Duddington, the Northampton Sand and Upper Lias clays again make their appearance in the valley of the Welland, at a distance of two miles from the points at which they have disappeared (Wakerley and Barrowden) owing to their southwesterly dip. Traces of the Northampton Sand are seen at Duddington, below the old pits which are said to have been worked for "slates." At Collyweston a number of wells have been sunk through the thick limestone beds of the Lincolnshire Oolite, and the underlying slates and sands, into the "red-rock" or ironstone of the Northampton Sand. The considerable supplies of water required in the working of the slate-pits are said to be obtained from the ironstone rock itself; it being found unnecessary to sink down into the clays of the Upper Lias. The beds of the Northampton Sand can also be traced on the opposite side of the Welland Valley at Ketton, but there offer no features of special interest. THE LOWER OOLITES. Along the sides of the Welland Valley to the westward, the beds of the Northampton sand are much obscured by masses of river-gravel, composed of oolitic detritus. They are seen again, however, at Wild's Ford opposite Tickencote Lodge, and at Ingthorpe. The springs at Wothorpe, which are collected in a reservoir for the supply of the town of Stamford, take their rise at the junction of the Northampton Sand and the Upper Lias Clay. A good section of the former beds is exposed in a deep road-cutting near this place. Along this part of the Welland Valley many landslips have taken place owing to the numerous springs which arise at the junction of the ironstone rock and the clays, and the facility with which the former, being undermined by this agency, slide over the latter. At the village of Easton the ironstones of the Northampton Sand are well exposed. The whole formation here is seen to have a thickness of about 20 feet. The striking "cellular" appearance presented by the ironstone rock is well exemplified at this point, and the connexion of this peculiar structure with the original jointing of the rock is here very manifest. This subject will be more fully treated of in the next chapter. The junction of the Northampton Sand with the Upper Lias Clay forming the channel of the River Welland is seen at this point. Very copious springs of water, which supply the village, are given off at the base of the ironstones. At Stamford, owing to the great east and west fault, the Northampton Sand which on the north side of the valley is at the level of the river, is on the south side exposed high up on the hill beside Burleigh Park. The whole of the beds exhibit signs of considerable disturbance. The ironstone and overlying sandy clays were exhibited at a number of points about the Midland and London and North-Western Railway Station at Stamford. At one point, where a small cross fault has thrown the sandy clays and ironstones of the Northampton Sand against the limestones of the Lincolnshire Oolite, a railway-cutting affords us a very interesting section (Fig. 7.) Figure 7. Section exposed in a railway-cutting at the Stamford Station of the a. Rubble Oolite. b. Oolite Limestone (Lincolnshire Oolite). c. Light-blue and white clays (Lower Estuarine Series). d. Ferruginous sands and ironstone (Northampton Sand). Higher up the hill Lumby's Terra Cotta Works expose an interesting section, which is as follows: (1.) Rubbly Oolite (in patches). (2.) Brown sand (irregular in thickness). (3.) "Terra-cotta clay," sandy and of a light blue colour, very irregular in thickness, 1 to 4 feet. (4.) Ironstone rock, 8 to 13 feet. (5.) Upper Lias Clay. The clay bed (3) has been analysed by Mr. Lumby (formerly a student in the Royal School of Mines). It is of a pale colour, and composed of almost pure silicate of alumina with a little free sand in very fine grains; sandy lumps also occur in the mass, which are ground up with the clay in the mill. This admixture of the clay with fine sand is said to greatly improve its quality. Mixed with a very small quantity of the white clay froin Poole, Dorsetshire, these clays of the Lower Estuarine Series make an excellent terra-cotta. Some years ago, in a futile attempt to find coal at this point, a boring was put down by the late Marquis of Exeter to the depth, it is said, of 500 feet. Unfortunately, however, no accurate record was kept of the beds passed through. From the information which I received, however, I infer that the Lias formation was not penetrated, no red rocks having been reached; if the information which I received can be relied upon, the Upper Lias Clay would appear to be about 140 feet in thickness at this place. Both the estuarine clays and sands, and the marine ironstones of the Northampton Sand are exposed at a number of points about Burleigh Park; and since the mapping of the area has been completed the quarrying of the latter as an iron-ore has been commenced by the Marquis of Exeter. (See Mr. Sharp's Paper in the Quart. Journ, of the Geol. Soc., vol. xxix. p. 273.) The light-coloured sands with ironstones at their base are seen at Wittering and many other points along the sides of the valleys of Southorpe and Thornhaugh, the beds being thrown far above their normal position by the great Stamford and Helpstone fault. At Ufford the white sands of the Lower Estuarine Series are found to be highly micaceous, and to contain many thin layers of lignite and fragments of wood. One of the pits at this point affords a very interesting section (Fig. 8). Figure 8. Section of the Northampton Sand seen in a pit east of Ufford, Northamptonshire. (a.) Oolitic limestone. (b.) Yellow, sandy limestone, with marine shells. (e.) White and fawn-coloured sands, with vertical plant remains, 3 ft. (f) Thin seams of lignite, together, 4 inches thick. (g.) Bed of very fine white sand, 1 ft. 6 in. h (h.) Yellow sands, becoming more and more ferruginous downwards, dug to 4 ft. (b) is similar to and corresponds with (a) of the section, Figure 9, on page 105. |