Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/255

1869.] iron band is seen gently undulating, and is traceable for a further distance of a mile in both an easterly and westerly direction. The " mineral " is mined by approximately level drifts, running N. 40° E. and at right angles to the face of the workings ; many of the levels have reached to a distance of two hundred yards.

The following section is in descending order, numbered from above : —

1. Hard, compact, columnar basalt. Where exposed to weathering influences, it is decomposed at the lower surface for a foot or so, within which there is an argillaceous mineral, probably a magnesian clay, termed by the miners " rock- grease."

2. Pisolitic iron-ore. This band consists of a dense red ochreous paste, with included spheroids, composed chiefly of a mixture of magnetite and red haematite. In the upper part of the band the spheroids are occasionally as large as hazel nuts, but more frequently of the size of peas, and densely crowded. The size and frequency of the nodules diminish downwards; Thickness 2 ft.— 2 ft. 6 in. and the ore passes into

3. Indurated ferruginous ochre, of a reddish-yellow colour, breaking up into irregular lumps Thickness 4 ft. It merges insensibly into the underlying band of

4. Lithomarge. A variegated rock, with a predominating blue colour and greasy feel, breaking up into small sub- spheroidal blocks. The whole mass might readily be mistaken from a distance for some of the variegated marls of the Keuper series Thickness 25 ft.

5. The lithomai'ge graduates downwards into a basalt exhibit- ing a concretionary structure, the outer coats not distin- guishable from the lithomarge, while the kernel is a com- pact basalt.

Fig. 1. — Section at Belumford.

2. Section at Belumford, north-west extremity of Island Magee:-

1. Columnar basalt, with two or three inches of decomposed rock below.

2. Pisolitic Iron-ore. The upper two inches with little or no ochreous matrix: the spheroids large, and now and then a thin lamina of the ore. The ochre increases in quantity with the increase of depth, and the iron-ore merges into 'bole' Thickness 2 ft. 6 in.

M 2