Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/535

1870.] SHARP NORTHAMPTONSHIRE OOLITES. 369 Area III. Duston.

The parish of Duston lies immediately west of Northampton, from which it is separated by the river and valley of the Nen. Its highest ground is capped with Great Oolite Limestone, A, which is quarried at Hopping Hill (q), about two miles N.W. of Northampton, on the Dunchurch road, and extends from that point in an irregular band for about a mile and a half nearly due west.

At about three-quarters of a mile N.E. of q, a nearly circular patch of this limestone, about a quarter of a mile in diameter, occurs upon the opposite high ground of the Dallington lordship (r), a deep valley and the Dallington brook intervening.

At about half-a-mile S. of q, another patch is quarried at s. This is on a somewhat lower level, having been let down in the fork of a double fault, marked in the map of the Survey.

At Hopping Hill (q), the limestone pit presents a section of about 12 feet elevation, the fossils obtained being in the bulk identical with those found in the Kingsthorpe limestone, the exception being that Pholadomya lyrata and P. Heraulti, forms not common at Kingsthorpe, are here very abundant. The earthy shale-bed ("Dirt Bed ") of Kingsthorpe is also present, but nearer the base than in the former section.

Section of Limestone A at Hopping Hill.

ft. in. ft. in.

1. Soft clay-like marl 2 0

2. Soft marly rock, in three layers of varying hardness, containing Pholadomya lyrata and P. Heraulti, &c 1 6 to 2 0

3. Band of soft marl, very full of shells 0 9

4. Hard marly rock, with few shells 1 0

5. Compact arenaceous stone, somewhat calcareous, with few shells, Ostrea costata, &c 1 3

6. Earthy shale-bed (" dirt-bed") in thin layers, containing flattened bivalves, chiefly Ostrea 1 0

7. Ditto, more argillaceous, and paler and greyer in colour 1 0

8. Very hard limestone, with blue heart, Rhynchonella concinna &c. ... 1 6

9. Soft limestone, very full of shells, Rhynchonella concinna, Modiola imbricata, Natica various species, large Nautili, Clypeus, &c. ... 1 6

Blue brick-clay at base.

At t, a little more than a furlong N.W. of the limestone-pit q, and on the N.W. incline of Hopping Hill, the underlying blue clay B is worked for bricks. It is here about 8 feet thick : at the top of the section is seen its junction with the overlying bottom soft bed of the limestone, and at the base the characteristic ferruginous band observable in the two former areas. This clay has occasional bituminous and woody bands and patches, but has yielded no other fossils.

In the same brick-field, within a very few yards, the underlying white sand C is dug to a depth of about 6 feet, but has not been bottomed. I have not found here the plant-bed, which probably has not been reached.

This sand forms the surface-bed over a considerably area of the opposite high ground to the N. and N.W., constituting the Dallington and Harlestone Heaths.