Chapter XXIII: Book VIII (4)

Alluvial mining--gold washing--being as old as the first glimmer of civilization, it is referred to, directly or indirectly, by a great majority of ancient writers, poets, historians, geographers, and naturalists. Early Egyptian inscriptions often refer to this industry, but from the point of view of technical methods the description by Pliny is practically the only one of interest, and in Pliny's chapter on the subject, alluvial is badly confused with vein mining. This passage (XXXIII, 21) is as follows: "Gold is found in the world in three ways, to say nothing of that found in India by the ants, and in Scythia by the Griffins. The first is as gold dust found in streams, as, for instance, in the Tagus in Spain, in the Padus in Italy, in the Hebrus in Thracia, in the Pactolus in Asia, and in the Ganges in India; indeed, there is no gold found more perfect than this, as the current polishes it thoroughly by attrition.... Others by equal labour and greater expense bring rivers from the mountain heights, often a hundred miles, for the purpose of washing this debris. The ditches thus made are called _corrugi_, from our word _corrivatio_, I suppose; and these entail a thousand fresh labours. The fall must be steep, that the water may rush down from very high places, rather than flow gently. The ditches across the valleys are joined by aqueducts, and in other places, impassable rocks have to be cut away and forced to make room for troughs of hollowed-out logs. Those who cut the rocks are suspended by ropes, so that to those who watch them from a distance, the workmen seem not so much beasts as birds. Hanging thus, they take the levels and trace the lines which the ditch is to take; and thus, where there is no place for man's footstep, streams are dragged by men. The water is vitiated for washing if the current of the stream carries mud with it. This kind of earth is called _urium_, hence these ditches are laid out to carry the water over beds of pebbles to avoid this _urium_. When they have reached the head of the fall, at the top of the mountain, reservoirs are excavated a couple of hundred feet long and wide, and about ten feet deep. In these reservoirs there are generally five gates left, about three feet square, so that when the reservoir is full, the gates are opened, and the torrent bursts forth with such violence that the rocks are hurled along. When they have reached the plain there is yet more labour. Trenches called _agogae_ are dug for the flow of the water. The bottoms of these are spread at regular intervals with _ulex_ to catch the gold. This _ulex_ is similar to rosemary, rough and prickly. The sides, too, are closed in with planks and are suspended when crossing precipitous spots. The earth is carried to the sea and thus the shattered mountain is washed away and scattered; and this deposition of the earth in the sea has extended the shore of Spain.... The gold procured from _arrugiae_ does not require to be melted, but is already pure gold. It is found in lumps, in shafts as well, sometimes even exceeding ten _librae_ in weight. These lumps are called _palagae_ and _palacurnae_, while the small grains are called _baluce_. The Ulex is dried and burnt and the ashes are washed on a bed of grassy turf in order that the gold may settle thereon."

[19] _Carbunculus Carchedonius_--Carthaginian carbuncle. The German is given by Agricola in the _Interpretatio_ as _granat_, _i.e._, garnet.

[20] As the concentration of crushed tin ore has been exhaustively treated of already, the descriptions from here on probably refer entirely to alluvial tin.

[21] From a metallurgical point of view all of these operations are roasting. Even to-day, however, the expression "burning" tin is in use in some parts of Cornwall, and in former times it was general.

[22] There can be no doubt that these are mattes, as will develop in Book IX. The German term in the Glossary for _panes ex pyrite_ is _stein_, the same as the modern German for matte. Orpiment and realgar are the yellow and red arsenical sulphides. The _cadmia_ was no doubt the cobalt-arsenic minerals (see note on p. 112). The "solidified juices" were generally anything that could be expelled short of smelting, _i.e._, roasted off or leached out, as shown in note 4, p. 1; they embrace the sulphates, salts, sulphur, bitumen, and arsenical sulphides, etc. For further information on leaching out the sulphates, alum, etc., see note 10, p. 564.