2170. The materials of which the path is composed, in the case of some houses, are mere planks, or lattice-work, supported on cross pieces of timber, in order to admit the sun and air to the soil below, and not to indurate it by the pressure of feet. An improvement on this mode consists in using grated cast-iron plates, which are more durable, and may be set on iron stakes driven in till their tops are on a level, and at a proper height, &c. These gratings are also particularly preferable when the path is over a flue, not only as presenting a cooler surface to walk on than the covers of the flue, but also by readily admitting the ascent of the heat in the interstices, and preventing the movement of the covers by the motion of walking. But the best material for a permanent path, as in greenhouses, botanic stoves, &c., is argillaceous flag-stone, and of this one of the best varieties is that obtained from Arbroath, and known by the name of Arbroath pavement It is a light grey schistus, which rises in laminï¾µ of from 3 to 6 inches in thickness, and 8 or 10 feet square; requires very little work on the surface; and has the property of but very slightly absorbing moisture from the atmosphere, or from the moist ground on which it may be placed. Thus, unless when watered on purpose, it always appears perfectly dry and agreeable, however moist the soil may be below. Where the paths in a house are on different levels, they are commonly united by steps; but an inclined plane, when not steeper than one inch in six, will generally be found more convenient for the purposes of culture and management; and if the slope is one in eight, it is more agreeable to ascend or descend than a stair.