The Old Red Sandstone of Scotland has been extensively employed for the purposes of the architect, and its limestones occasionally applied to those of the agriculturist. As might be anticipated in reference to a deposit so widely spread, the quality of both its sandstones and its lime is found to vary exceedingly in even the same beds when examined in different localities. Its inferior conglomerate, for instance, in the neighborhood of Cromarty, weathers so rapidly, that a fence built of stones furnished by it little more than half a century ago, has mouldered in some places into a mere grass-covered mound. The same bed in the neighborhood of Inverness is composed of a stone nearly as hard and quite as durable as granite, and which has been employed in paving the streets of the place--a purpose which it serves as well as any of the igneous or primary rocks could have done. At Redcastle, on the northern shore of the Frith of Beauly, the same conglomerate assumes an intermediate character, and forms, though coarse, an excellent building stone, which, in some of the older ruins of the district, presents the marks of the tool as sharply indented as when under the hands of the workman. Some of the sandstone beds of the system are strongly saliferous; and these, however coherent they may appear, never resist the weather until first divested of their salt. The main ichthyolite bed on the northern shore of the Moray Frith is overlaid by a thick deposit of a finely-tinted yellow sandstone of this character, which, unlike most sandstones of a mouldering quality, resists the frosts and storms of winter, and wastes only when the weather becomes warm and dry. A few days of sunshine affect it more than whole months of high winds and showers. The heat crystallizes at the surface the salt which it contains; the crystals, acting as wedges, throw off minute particles of the stone; and thus, mechanically at least, the degrading process is the same as that to which sandstones of a different but equally inferior quality are exposed during severe frosts. In the course of years, however, this sandstone, when employed in building, loses its salt; crust after crust is formed on the surface, and either forced off by the crystals underneath, or washed away by the rains; and then the stone ceases to waste, and gathers on its weathered inequalities a protecting mantle of lichens.[AW] The most valuable quarries in the Old Red System of Scotland yet discovered, are the flagstone quarries of Caithness and Carmylie. The former have been opened in the middle schists of the lower, or Tilestone formation of the system; the latter, as I have had occasion to remark oftener than once, in the Cornstone, or middle formation. The quarries of both Carmylie and Caithness employ hundreds of workmen, and their flagstones form an article of commerce. The best building-stone of the north of Scotland--best both for beauty and durability--is a pure Quartzose Sandstone furnished