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those of any other colour; and that the stone should besomewhat harder than the pencil, that the marks may pro-ceed chiefly from the pencil, without scratching the sub-stance of the stone.

The only native blacks I know of, that have been em-ployed as colouring materials, are the following.

I. Black chalk.

The black chalk or black marking-stone of the shops,.so called from its use in drawing black lines, on paper, isa light earthy substance, of a pretty deep black colour,moderately firm, in texture somewhat flaky like slate, notof a rough harsh surface like common chalk, but rather,soft and smooth to the touch. It stains very freely, and,.in virtue of its smoothness, makes very neat marks. It iseasily reduced into an impalpable soft powder, without anyapparent diminution of its blackness. In this state, itmixes easily with oil into a smooth paste; and being dif-fused through water, it slowly settles, in a black slimy ormuddy form; properties which'make its use very con-venient to the painter both in oil and water colours. En-tire masses of it, laid in water, are also by degrees pene-trated and disunited, though much more difficultly than.those of white chalk.

It appears, in effect, to be. an earth of a quite differentnature from common chalk, and seems to be rather of theslaty bituminous kind.. In the fire it becomes, white witha reddish cast, and very friable.; retaining its flaky structure,and looking much like the white flaky masses which somesorts of pitcoal leave in burning. Acid liquors neither dis-solve, nor alter the colour of the black chalk itself; norhave they, so far as I could observe, any sensible actionupon the white ashes.

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