Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/543

1870.] SHARP — NORTHAMPTONSHIRE OOLITES. 377 headland, occupying the angle formed by the junction of the Nen valley with the broad valley through which passes the London and North-western railway. The road from Northampton to Blisworth ascends this hill, and passes over the junction of the Upper Lias with the lower beds of the Northampton Sand, marked by the presence of springs. On the ridge, near the Danes' Camp, is a small patch of Great Oolite Limestone at aa ; and upon the descent on the southern side, at bb, the junction of the white sand C with the beds D is observable. In the valley below, the Marlstone of the Middle Lias is the prominent surface-bed.

At a distance of five miles from Northampton, in this direction, is

Area IV. Blisworth.

The general section of this area varies in some particulars from that of each of the areas I have yet described. The high grounds are capped with a thick bed of Boulder-clay, containing rounded boulders of primary rocks, fragments of chalk and flints, masses of Septaria, rounded blocks of indurated Oxford Clay enclosing numerous Ammonites and other fossils, &c.

Between the Boulder-clay and the underlying Great Oolite Limestone, A, is a bed of very variegated and thinly stratified Great-Oolite clay, very full of small oysters (Ostrea subrugulosa). This clay occurs also in the same position at Tiffield, about two miles S.W., and at Stowe Nine Churches, some six miles west. At the latter place it is seen at the top of the section of a mass of Great Oolite let down by a fault below the level of the neighbouring ironstone ; the wall of which fault, sharply defined, is seen in the quarry. I have indicated the place of this clay in my General Section by the letter X.

Another variation consists in the remarkable thinning of all the beds between the Great-Oolite limestone, A, and the lower beds, E, of the Northampton Sand. These beds, B, C, D, which represent in the General Section an aggregate thickness of from 55 to 60 feet, have here dwindled to a thickness only of from 8 to 10 feet. They have again thickened, however, in districts S. & S.W. of Blisworth.

A section of the Great-Oolite limestone is graphically seen in the cutting of the railway between the Blisworth and Roade stations ; but it may be more particularly examined in the ancient and large quarry to the S.E. of the village. This quarry is approached from a point near to the N.E. entrance of the great tunnel of the Grand Junction Canal ; which tunnel, cut to a length of nearly two miles in the Upper Lias clay, constituted one of the great engineering works of the last age.

The following is the section in this quarry : —

Section of the Blisworth Great-Oolite Limestone Quarry, with Quarrymen's Terms. ft. in. ft in.

1. Boulder-clay 11 0 to 12 0

2. " Rammel " — clay, very variegated (green, yellow, brown, blue, and black), thinly stratified, full of Ostrea subrugulosa, and containing wood 1 6 to 2 0

VOL. XXVI. — PART I. 2 D