T R I P E L A S.

falls from it in large irregular masses, leaving an even but somewhat rough surface behindit; when dry, it is of a pale whitish or rather greenish red, of a loose spungy texture, andremarkably light; it is of a rough, uneven, dusty surface, adheres slightly to thetongue, is hard, dry and harsh to the touch, easily breaks to pieces between the fin-gers, and dusts, but does not stain the hands; in rubbing between the fingers it yieldssomething of the same harsh sound with the greyish kind before describ’d, but in amuch less degree ; it breaks very freely in the mouth, and is harsh and dry between theteeth; thrown into water, it makes a very brisk ebullition and hissing, but does not rea-dily moulder in it.

View’d by the Microscope, it appears of a dusty spungy texture, more loose and openthan any of the before describ’d.

It makes no effervescence with Acids, and suffers not the least change in the fire.

I have observ’d it in Devonshire, Dorsetshire, and Somersetshire, and particularlyplenty in a pit in the way from Bath to Mendip-Hills; it is also found in France andSpain, and in America. It is a fine substance for polishing stones: I have try’d it,and find it nearly equal to the yellowish Tripela, and much superior to the commonRottenstone which the lapidaries now commonly use.

Sect. II. The Brownish T R I P E L A S.

i. 'Tripela fuse a levis .

Light brown Tripela.

T HIS is the substance which our workmen call Rottenstone.

While in the earth it is soft, moist and very crumbly, easily cut thro’with the spade, but falling in rude masses, and leaving a rough surface behind it ;when dry; it is of a dusty brown, very light, and of a considerable hardness; it is of aloose spungy texture, and of a rough, irregular and dusty surface, it adheres slightly tothe tongue, is dry, harsh and rough to the touch, does not break very easily betweenthe fingers, and but slightly stains the hands; in rubbing it yields a little harshish sound;it breaks freely in the mouth, and is dry and harsh between the teeth; thrown intowater, it makes a brisk ebullition and hissing, but does not readily moulder awayin it.

View’d by the Microscope, it appears of a harsh, loose texture.

It makes no effervescence with Aqua Fortis.

In the fire it burns to an additional hardness, and pale and something reddishcolour.

It is dug in Derbyshire, Shropshire and Somersetshire, and is of great use amongour brasiers and lapidaries, who now constantly use it in polishing.

2. Tripela pallide fusca dura.

Hard , pale brown Tripela.

This is a very hard, dry and harsh Earth. While in the stratum it is too hard to becut with the spade; it is dug with pick-axes, and falls in rude large masses : but it is notunfrequently found also naturally loose and in detach’d pieces; when dry, it is of a verypale brown, sometimes with a faint cast of reddissiness ; moderately heavy, of a closecompact texture, and almost a stony hardness; it is of a smoother, more even, and lessdusty surface than most of the other Tripelas; it adheres slightly to the tongue, is dry andrough to the touch, is not to be broken between the fingers, and slightly stains the hands jit breaks freely in the mouth, and is harsh and gritty between the teeth, seeming morehard and coarse than any of the former except the grey. Thrown into water, itmakes a slight ebullition and hissing, but does not easily fall to pieces in it.

View’d by the Microscope, it is of a more compact texture than any of the former,and usually seen to contain some small slakes of a sebaceous Talc, which are inseme specimens also visible to the naked eye.

It makes no effervescence with Aqua Fortis.

In the fire it burns to a pale reddish colour without any additional hardness,t is dug in Wiltshire, and some other parts of England, and is common in Francean many other parts of the world; it is us’d among artificers in the fame manner asthe common Rottenstone.

3. 'Tripela

T