When they have reached the level ground, too, there is still another labour that awaits them. Trenches—known as “agogæ”[895]—have to be dug for the passage of the water; and these, at regular intervals, have a layer of ulex placed at the bottom. This ulex[896] is a plant like rosemary in appearance, rough and prickly, and well-adapted for arresting any pieces of gold that may be carried along. The sides, too, are closed in with planks, and are supported by arches when carried over steep and precipitous spots. The earth, carried onwards in the stream, arrives at the sea at last, and thus is the shattered mountain washed away; causes which have greatly tended to extend the shores of Spain by these encroachments upon the deep. It is also by the agency of canals of this description that the material, excavated at the cost of such immense labour by the process previously described,[897] is washed and carried away; for otherwise the shafts would soon be choked up by it. The gold found by excavating with galleries does not require to be melted, but is pure gold at once. In these excavations, too, it is found in lumps, as also in the shafts which are sunk, sometimes exceeding ten pounds even. The names given to these lumps are “palagæ,” and “palacurnæ,”[898] while the gold found in small grains is known as “baluce.” The ulex that is used for the above purpose is dried and burnt, after which the ashes of it are washed upon a bed of grassy turf, in order that the gold may be deposited thereupon. Asturia, Gallæcia, and Lusitania furnish in this manner, yearly, according to some authorities, twenty thousand pounds’ weight of gold, the produce of Asturia forming the major part. Indeed, there is no part of the world that for centuries has maintained such a continuous fertility in gold. I have already[899] mentioned that by an ancient decree of the senate, the soil of Italy has been protected from these researches; otherwise, there would be no land more fertile in metals. There is extant also a censorial law relative to the gold mines of Victumulæ, in the territory of Vercellæ,[900] by which the farmers of the revenue were forbidden to employ more than five thousand men at the works. CHAP. 22.—ORPIMENT. There is also one other method of procuring gold; by making it from orpiment,[901] a mineral dug from the surface of the earth in Syria, and much used by painters. It is just the colour of gold, but brittle, like mirror-stone,[902] in fact. This substance greatly excited the hopes of the Emperor Caius,[903] a prince who was most greedy for gold. He accordingly had a large quantity of it melted, and really did obtain some excellent gold;[904] but then the proportion was so extremely small, that he found himself a loser thereby. Such was the result of an experiment prompted solely by avarice: and this too, although the price of the orpiment itself was no more than four denarii per pound. Since his time, the experiment has never been repeated.