OF EARTHS. 45 



moulders into a fine foft powder. It does not effervefce with 

 Aquafortis. In the fire it crackles a little, and acquires a con- 

 fiderable additional hardnefs, and a paler colour. It is much ufed 

 in painting. 







A fine black clay-ochre, with a bluifh-caft (I), is in a fear at 

 the eaft end of the rectory-den at Simonburn. It is near the top, in 

 a vein of about feven inches thick, under a ftratum of limeftone, 

 and above another of grey and yellowifh-white fand. Towards 

 the middle are large heavy mafTes of friable freeftone, and under 

 them large flags. Many of the freeftone mafles lie fcattered at 

 the foot of this great fteep, tumbled down by ilorms and frofts, 

 mattered and broken, mewing numerous impreflions of the bark 

 of rcfmous trees, of a tawney black colour. Many of the flags 

 are deeply channelled by the dripping of the water; others 

 fmooth and thick, of a great fize, not unfrequently two or three 

 yards long, and as many broad ; large pieces of fulphur in them 

 as big as walnuts. This and the fand lie among them promifcu- 

 oufly. The ochre with the leaft preffure between the fingers 

 breaks into thin flakes or lamella:, of a fmooth glofly furface, 

 unctuous to the touch, and flightly flaming the hands. It ad- 

 heres to the tongue, melts freely in the mouth, of an infipid 

 tafle, with very little grittinefs. In water it makes a flight ebul- 

 lition, feparates into fmall tabular pieces, and moulders by de- 

 grees into a fine powder, and gives it a bluifh-black colour. 

 Depurated, and worked into a pafte, it cuts through with a glofly 

 furface. Dry, it retains its colour, and drawn on paper or a 

 board marks a line of the fame tinge. It does not effervefce 



(I) Ochra nigra argillacea. Da Cofta. Nat. Hift. Fofl'. p. 89. No. i. 

 Ochra nigricans argillacea. Charlet. deFofT. p. 219. No. 4. 

 Humus nigra pictoria, Atramentum fciflile. Waller. Minero!. Spec. 4. 

 Argilla nigrefcens friabilis levis. Hill. Hift. FofT. p. 34. No. i. 



with 



