Slate, a fossil, consisting of a compact stone, that may be split into thin plates.

There are several varieties of this mineral, chiefly distinguished by their colour, which is in general grey, intermixed with blue, green, or black streaks ; though sometimes purplish, yellowish, brown, bluish-black ; and occasionally streaked with a darker hue than the ground itself.

Slate constitutes a part of many mountains : it is found in some counties of Britain, and Ireland, near the surface of the soil: the largest masses of it, however, are dug out in the Island of Eusdale, one of the Hebrides, whence slate is annually exported to England, the West Indies, etc. to a considerable amount.

The chief purpose to which slates are applied, is that of covering houses ; for which it furnishes a ng and elegant roof. As the usual method of slating has, from experience, not proved sufficiently durable, Mr. Richard Elliott obtained a patent in March, 1781, for a mode of covering houses, etc. on a more safe and eligible plan than that generally followed. His practice consists in cutting the slates in a rhomboidal form, so as to fold over each other. These are next laid in lime or putty, and fastened to the rafters, on boards, by means of nails or screws, either of wood or iron. This patent is now expired : and, as Mr. Elliott's method promises to secure houses vered with this fossil more effectu-ally from the effects of rain and moisture, than the common plan, we recommend the former to the attention of our readers ; referring such as may wish for a more tinct idea of his practice, to the 12th vol. of the Repertory of Arts ; where it is fully described, and illustrated with an engraving.