Of earth.

9

J^ow, besides the description and characters we have given of theseseveral Moulds and Earths, as they reside in their several beds and couches,there are divers other indications, by which we may discover their quali-ties and perfections; as, amongst others, a most infallible one is, theirdisposition to melt and crumble into fine morsels, not turn to mud andmortar, upon the descent of gentle showers, how hard soever they seembefore, and if in stirring they rise rather in granules, than, mafsy clods.

If upon excavating a pit, the mould you exhaust do more than fill itagain, Virgil tells us it is a good augury; upon which Laurembergiusaffirms, that at Wittemberg, in Germany, where the Mould lies so close,

together. They do not burn, nor are they malleable; are easily diffusible, but not soluble,in water. Properly there are but two sorts :

I. Argillaceous Earths, which harden in the lire, and do not difsolve in the mineral acids.

II. Ale aline, or Calcareous Earths, which in the fire burn to lime, and difsolve in the mineral

acids.

Argillaceous Earths consist aitlier of spongeous, or of smooth tenacious

parts : the former is called y'egeta&le liarth, or Mould the latter Clay.

Among the Clays are reckoned:

I. Potters’ Earths , viz.

1. Loam , which is coarse, irony, and very sandy.

2. Common potter’s day, which is heavy, without sand, of different substance and

colour, whence some require a greater degree of heat to flux them than others.5. Fine clay, or porcelain clay, which,is smooth and greasy, to the touch, and of va-rious colours.

JI. Medicinal Earth, viz.

1. Boles and Terras Sigillatae,

III. Mechanical Earths, viz.

1. Tripoli.

2. Fuller’s Earth, which lathers like soap, and raises a froth in the water. But thetrue Fuller’s Earth difsolves in acids, and consequently belongs to the Marl-Earths.

1 .

2 .

IV. Painters ’ Earths, viz-

White.

Mineral yellow.Umber.

4. Mineral red.

5. Mineral blue.

6. Mineral green.

To the Alcalde or Calcareous Earths belong the following:

I Chalk This is composed of fine particles, adhering closely together, and forming a' pretty compact texture. It colours the hand upon being touched, and commonly

is white, but sometimes is of different colours and kinds.

II Marls These are of a loose, friable texture, easily reducible into powder, and

^readily separating and diffusing in water. When recently dug out of the ground,

Volume II. ^ ^