Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/266

 traced in it the existence of alumine, of lime, of magnesia, of oxyd of iron, and of silica. It feels greasy and smooth, its colour varies from ash-grey to blue, its fracture is a little shining and uneven. It contains sometimes cylindrical blue nodules (called pins by the workmen) of a more close texture, in which there is probably a greater proportion of oxyd of iron. This clay is sent to Staffordshire, where it is mixed with ground flints, and employed in the finer kinds of pottery. I found the specific gravity of one of the purest specimens from Threshers's clay-pit, 1.723. Mr. Kirwan states potters' clay to be from 1,8 to 2.

I have been informed by very competent persons that the beds of clay in the trough of Poole do not affect any particular direction.

The situation of the potters' clay in this present instance, is perfectly agreeable to Werner's opinion.

(c) Coaly bituminous matter.

Remains of vegetables, some of which still retain their texture and shew that they belonged to the tribe of aquatic plants, are to be found in a white quartzose sand impregnated however with oxyd of iron, in the cliffs of the south-western coast of the Isle of Wight: at the east of Freshwater bay, some scaly carbonated wood with iron pyrites, is also to be found in the sand.

An earthy brown-coal extremely friable, and which crumbles to pieces when put into water, underlies the potters' clay in the sandy trough of Poole, where it forms a seam of some thickness. It burns with a weak flame emitting a particular and rather fragrant smell of bitumen, somewhat analogous to that of the Bovey coal. They differ however in point of specific gravity, this being 1,153, while Bovey