110	AURUM.
	(which they call ' gangadias') that is almost impenetrable. This they attack with wedges of iron, and mallets of the same metal, and think nothing is so hard—were it not that the thirst for gold is of all things the very hardest. When the works are finished they cut through from below the supports of the arches. The coming fall gives warning, but that is only intelligible to the look-out stationed upon the top of the hill itself. He by shout­ing, by waving his hand, gives the signal to call out the miners, and at the same time flies down himself. The hill, crushed, falls in with a crash that cannot be conceived by human imagination, emitting a blast of wind of incredible violence. The successful miners view triumphantly the ruins of nature. Nevertheless the gold is not yet got, nor were they certain it existed there all the time they were excavating : a sufficient motive for all their risk and expense was the hope for what they desired. " Now comes another task equal in difficulty, and of even greater expense. They conduct streams, in order to wash this wreck, along the mountain-ridges (an extra work), often from a distance of a hundred miles. This canal they call ' Conrugos,' probably a name derived from conrivatio. Here also there are a thousand labours to be encountered. The inclination of the level must be steep, so that the water may rush rather than flow ; and therefore they conduct it from the highest parts. The inter­vening valleys and ravines are bridged over by a watercourse in masonry ; in other places impassable rocks are excavated, and forced to yield a support for hollowed trunks of trees conveying the water. The workman, as he cuts, is suspended by a rope, so that to the distant view he presents the appearance not even of an animal, but merely of a bird on the wing. For the most part the engineer is suspended by a rope as he takes the levels and marks out the line for the canal; and where there is not even place for a man's foot to stand, rivers are led along by man's in­genuity. It spoils the washing if the stream bring any mud with it (that is a sort of earth which they call ' Urium'), for which reason they conduct the water over rocks and pebbles, and avoid the ' Urium.' At the ends of the fall upon the slope of the hills they excavate reservoirs 200 feet square, and 10 deep. In these, five outlets, usually 3 feet square, are left: so that when