Another remarkable slate-quarry in France, is situated near Angers. The bed of slate extends for a space of two leagues, passing under the town of Angers, which is in great part built of slate; those blocks which are the least divisible being employed in masonry. The quarries actually explored are all in the same line, from west to east, as well as the ancient pits, the bed of the best roof-slate rising to the surface in this direction. Immediately under the vegetable earth is found a brittle kind of slate, which, to a depth of four or five feet, splits into rhomboidal fragments. A little lower is the building-stone, which is a finer but scarcely divisible slate, and is employed in the construction of houses, after it has been sufficiently hardened by exposure to the air. At fourteen or fifteen feet from the surface is found the good slate, which has been quarried to the perpendicular depth of three hundred feet, without its lower limit being attained. The interior structure of the slaty mass is divided by many veins or seams of calcareous spar and quartz, fifteen or sixteen feet in length, by two feet thick; these veins are parallel, and proceed regularly from west to east in a position rising seventy degrees to the south; they are intersected by other veins at intervals of a similar kind, but whose rise is seventy degrees north; so that when the two series meet, they form rhombs or half-rhombs. All the layers or laminæ of slate have a direction similar to those of the veins of quartz, so that the whole mass becomes divided into immense parallel rhomboids. The slate is extracted in blocks of a determinate size, which are then divided into leaves for roof-slates. When the blocks have been drawn from the quarry, if they are left exposed to the sun or the open air, they lose what is called the _quarry-water_, and then become hard and untractable, and can only be employed as building-stone. Frost produces a singular effect on these blocks; while frozen, they may be broken with more ease than before; but if thawed rather quickly, they become no longer divisible; yet this quality may be restored by exposing them once more to the frost. The Process of Slating. When the blocks of slate for roofing have been split, and the laminæ roughly squared, they are sorted, according to their size and quality, and are brought to market under the quaint names of _Imperial slates_, _Duchesses_, _Countesses_, &c., the first variety being the largest. The best roofing-slates come from the celebrated vale of Festiniog.