Of EARTHS. 43 



the opinion of Dr. Woodward (g), and only rivalled by the Stur- 

 bridge-clay. It has been worked for many years, and ftill holds 

 its reputation. The mine is about twenty fathom deep ; the clay- 

 vein three feet thick, under a variety of flrata, one of coal ; it is 

 lett, worked, and fold by the ton ; yielding 3 1. per ton. 



On Acome-Fell, near Hexham, is a brown argillaceous earth, 

 with a yellowifh. caft. It is harm to the touch, tough, and duc- 

 tile. Thrown into water, it makes an ebullition, with a flight 

 noife, and after fome time moulders to a powder, a little gritty. 

 It effervefces with Aqua fortis. In the fire it acquires a dull red- 

 difh-brown. It was lately ufed in making a fine black carthern 

 ware, by a perfon well fkilled in the figuline art from Stafford- 

 Jhire. 



The Rubrica molliufcula, thefofter reddle (h), is not unfrequent. 

 It is heavy and o a compact texture, unctuous, and flaining the 

 fingers ; harm to the tafte, and fomewhat gritty. It is diffufible 

 in water, and gives it a deep claret colour. Depurated, and 

 worked into a pafte, it cuts through with a glolTy furface. It 

 does not effervefce with Aquafortis. In the fire it acquires no 

 change of colour. It is the foft clay iron-ore of Dr. Woodward (I). 

 The miners call it the Mother of the Mine. Others call it Smit, 

 from their marking their flieep with it. It is ufed by pain- 



(g) Cat. of Fofll 



(h) Argilla faturate rubra un&uofiffima. Da Cofta. Hifl. Fofl*. p. 5. No. 3. 

 Marga ponderofa rubra mollis, qu<e rubrica fabrilis Authorum. Hill. Hift. FofT. p. 47, 

 No. j. 



Rubrica fabrilis. Merret. Pin. Rer. Nat. Brit. p. 218. 

 Charlet. de Foff. p. 219. No. 3. 



(/) Woodw. Meth. of Foff. p. 2. No. 6. 

 Cat. A. 95, et 96. 



G s ters, 



