22 CLAYS.

leaves a considerable grittyness between the teeth, but the particles that occasion itseem not large.

Examin’d by the Microscope it appears a loose Clay, containing a considerable quan-tity of a small pale brown sand.

It makes no effervescence with Aqua Fortis.

In a moderate fire it acquires a reddish brown colour without much hardness: Ina violent one it is converted into a coarse green glass.

It is dug in Staffordshire, and us’d there by the potters ; and is also sound in mostother counties: This and the former earth, which are neither of them alone very fitfor the potters use, are mix’d with some of the purer and stiffer Clays to be describedhereafter, to break their texture, and make them easier to work for the coarser vessels.

11 . Argilla indurata albo-purpurea lœvis , Steatites recentiorum , Cimolia

purpurafcens antiquoriun.

Smooths purple , and white indurated Clay , the Steatites of the moderns,

the purple Cimolia of the antients.

This is the Steatites Aldrov. Musi Met. 665. Steatites Wood, Vol. 1. P. 6. a 20,21. And is evidently the Cimolia purpurafcens of the antients.

This and the three following substances, tho’ from their great hardness they mightappear to some of a different class of Fossils; yet upon a strict examination, are found tohave all the properties of a harder Clay, and are therefore strictly and properly of this.

This species is a most elegant and valuable Earth, compos’d of extreamly fine particles,of a firm, equal and regular texture, and very great weight.

While in the stratum it is considerably hard, and will not be cut down evenly with thespade, as most of the Clays are, but breaks irregularly into lumps of different strapsand size, and after it has been some time taken out, becomes yet much harder.

It is of a perfectly fine smooth and glosiy surface, softer and smoother to the touchthan any of the other Earths, and does not at all adhere to the tongue, or stainthe fingers in handling, but drawn along woollen cloth, or any other rough sub-stance, leaves a fine and clean white line : It is in colour white, beautifully vein’d withpurple of different degrees of deepness ; and of so fine a structure of parts, That cut in-to thin pieces it is in some degree transparent. It is very difficulty diffusible in water,and melts but slowly in the mouth, filling it with a smooth unctuous softness, and notcontaining the least hard particle, or leaving the slightest grittyness between the teeth.

Examin’d by the Microscope it appears one regular and uniform mass, a little moreopake in the purple parts than in the white, and so perfectly equal in all its parts, thatthe best glasses can discover no blemish in its texture.

It raises no effervescence with Aqua Fortis.

It burns to a great hardness and whiter colour; and in a violent fire to a pure white glass.

It is dug in many parts of Devonshire, Cornwal, and the neighbouring Counties;the cliff of the Lizard Point is almost wholly compos’d of it, and the adjacent littleislands abound with it; the people of Cornwal from its colour, smoothness and con-sistence, resembling those of the common hard soap, call it soap rock; and the lateauthors in general have called it Steatitis, from suet, because of its resemblance tothe hard fat of animals. The antients gave it the name of Cimolia, from the islandwhere it was then most frequently found.

This is of all the English Earths the most worthy making trials of, for the imitating thefine Porcelain ware of China; Dr. Woodward much recommends it on this account, andrepeated trials have been since made of it, and some of them very lately, in all which ithas afforded the finest earthen ware ever made with us; and promises fair for equalling,with right management, any in the world.

12 . Argilla indurata albo-virefcens levis 5 quœ Morochthus antiquorum .

Smooth , green and white indurated Clay , called Morochthus.

This is Me Lapis Morochthus Boet. 411. De Laet. 140. Mathiol. 13 85. Musi Calc.275. Morochthus.aliis Leucogæa, Leucographis, Galaxius, Graphida Galactites. Worm.71. Charlt. 30. Morochthus Aldrov. Musi Met. 668. Agricol. 606, and the MorochtisMerqctes or Morochites of Pliny.

It