Mines of silver,[2] gold, and precious stones were also fairly numerous in Spain. Moorish authors wrote enthusiastically of the mines of precious metals in or close to the Sierra Nevada. "Even at this day," said Bowles, "the Moorish mines may be distinguished from the Roman. The Romans made the towers of their fortresses of a round shape, in order to avoid as far as possible the blows of the battering-ram; and their miners, whether from habit or intentionally, made the mouths of their mines round also. The Moors, as strangers to this engine, built their towers square and gave a square shape also to the mouths of their mines. The round mouths of Roman mines are yet to be seen at Riotinto and other places, and the square mouths of Moorish mines in the neighbourhood of Linares." [2] "I am not aware of any Spanish mine containing silver in a state of absolute purity; though some, I think, would be discovered if they were searched for."--Bowles: _Historia Natural de España_. Emeralds were formerly extracted from a mine at Moron, in the Sierra de Leyta; white sapphires and agates at Cape de Gata,[3] at the eastern extremity of the Gulf of Almeria; amethysts at Monte de las Guardas, near the port of Plata, "in a precipice (_sic_) about twenty feet in depth." According to Laborde, garnets have been discovered down to modern times "in a plain half-way on the road from Almeria to Motril. They are very abundant there, particularly in the bed of a ravine, formed by rain-torrents, at the foot of a little hill, upon which a great number of them are likewise found. The emeralds are in the kingdom of Seville, all the others in that of Granada. It has been said for some time that a pit in the mountain of Bujo, at Cape de Gata, contains a great many precious stones; but none could be found there, notwithstanding the prolonged and careful searches that were lately made." [3] Possibly, as Bowles suggests, for Cabo de Agata--"Agate Cape." "It would not be strange," he adds, "if diamonds were found at this cape, since there are signs of their presence. I found white sapphires, slightly clouded, together with cornelians, jaspers, agates, and garnets."