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Rh are exposed before his eyes. There are just as great differences in hills as there are in mountains, yet the miner does not dig except in those situated in mountainous districts, and even very rarely in those. It is however very little to be wondered at that the hill in the Island of Lemnos was excavated, for the whole is of a reddish-yellow colour, which furnishes for the inhabitants that valuable clay so especially beneficial to mankind. In like manner, other hills are excavated if chalk or other varieties of earth are exposed, but these are not prospected for.

There are likewise many varieties of valleys and plains. One kind is enclosed on the sides with its outlet and entrance open; another has either its entrance or its outlet open and the rest of it is closed in; both of these are properly called valleys. There is a third variety which is surrounded on all sides by mountains, and these are called convalles. Some valleys again, have recesses, and others have none; one is wide, another narrow; one is long, another short; yet another kind is not higher than the neighbouring plain, and others are lower than the surrounding flat country. But the miner does not dig in those surrounded on all sides by mountains, nor in those that are open, unless there be a low plain close at hand, or unless a vein of metal descending from the mountains should extend into the valley.

Plains differ from one another, one being situated at low elevation, and others higher, one being level and another with a slight incline. The miner should never excavate the low-lying plain, nor one which is perfectly level, unless it be in some mountain, and rarely should he mine in the other kinds of plains.

With regard to the conditions of the locality the miner should not contemplate mining without considering whether the place be covered with trees or is bare. If it be a wooded place, he who digs there has this advantage, besides others, that there will be an abundant supply of wood for his underground timbering, his machinery, buildings, smelting, and other necessities. If there is no forest he should not mine there unless there is a river near, by which he can carry down the timber. Yet wherever there is a hope that pure gold or gems may be found, the ground can be turned up, even though there is no forest, because the gems need only to be polished and the gold to be purified. Therefore the inhabitants of hot regions obtain these substances from rough and sandy places, where sometimes there are not even shrubs, much less woods.

The miner should next consider the locality, as to whether it has a perpetual supply of running water, or whether it is always devoid of water except when a torrent supplied by rains flows down from the summits of the mountains. The place that Nature has provided with a river or stream can