Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/285

 this are three beds of the Great Oolite series, having a maximum thickness of 45 feet — the lowest consisting of clay having a persistent

Fig. 1. — Diagram of General Section, slioiving the 'position of the Inferior Oolite Limestone and Divisions of Northampton Sand.

Blisworth Clay ( 2 ft.).

White Limestone (25 ft.)

Blue Clay (15 ft.)

Ferruginous band

Place of Great Limestone of the Inferior Oolite

Upper ( White Sand (12 ft.)

Plant-bed

Great Oolite. Line of unconformity.

Middle Variable beds (30 ft.) Limestone. Slate

Lower Beds containing Ironstone (4 ft.) Amm- bifrons bed Pebbly bed Upper Lias.

ferruginous band at its base (which clay, containing wood, plants, and numerous bands with fresh-water shells, and exhibiting other estuarine characteristics, has been termed by Mr. Judd the " Upper Estuarine Series ") ; the middle, of a series of marly limestones ; and the uppermost, of clay characterized by an abundance of Ostrea subrugulosa.

The Middle Division of the Northampton Sand was separated by me from the Lower Division (provisionally, as I stated) because of the intervention of a band of coarse Oolitic Limestone, and because of differences, throughout the district then treated of, in their mineral and stratigraphical characteristics.

To the north-east of Northampton, however, those differences are not so marked : for instance, over a considerable area, in the Lower Division, for ironstone is substituted an only slightly ferruginous limestone ; and again, in other places, the Middle Division is quarried for ironstone, being more richly ferruginous than the Lower Division, while the Limestone band is frequently absent.

In contrast to the varying, and therefore uncertain, marks of distinction between the Lower and Middle Divisions of the North-

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