254 Dr. Berger on the Geology of some parts 



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 work- 

 men) of a more close texture, in which there is probably a greater 

 proportion of oxyd of iron. Tliis 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 per- 

 fectly agreeable to Werner's opinion, f 



(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 M'ith 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 



* Elements of Mineralogy, toI. i. p. 130. 

 + lirochant; Traits do Miiicialogie, tome i. p. 325. 



