In Victoria the most prolific gold-fields are in regions where the old formations are pierced by igneous rocks which have flowed from extinct volcanoes; and some of the richest alluvial deposits have been found on the pipe-clay bottom of flat, wide-spread plains, or settled in great subterranean gutters, under broad, elongated slopes, which the miner can reach only by sinking his shaft through stratum after stratum, from fifty to three hundred feet down, before he reaches the buried treasure. The inference necessarily is that much of the gold-drift of Australia is of an earlier origin than the deposits of California, which are the products of the existing mountain ranges, and therefore will be exhausted in a comparatively brief period. In Victoria, not seldom three distinct auriferous deposits, the result of successive upheavals and depressions, occur in the same locality; and the miner finds, in the course of his working, a first, second, and third bottom, the last being always on the solid and unmoved palæozoic rock, from which all the gold has been derived. Rich as the auriferous drifts of the deep alluvial deposits are frequently found to be, they must be within definite limits, having been deposited by currents and the continuous action of waves not far from the localities where the gold was originally formed. But the alluvial gold of Victoria and New South Wales is not confined to drifts and gutters. There are hundreds, probably thousands, of square miles, where the clay, earth, and sand are impregnated with gold in sufficient quantities to pay well for washing. Besides these deposits of incalculable wealth, there are vast reserves of gold locked up in the great mountain ranges both of Victoria and New South Wales, the hidden wealth of which will eventually be brought to light by systematic mining. As even the richest auriferous drift would be comparatively worthless without the assistance of water, the diversion of a running stream through a ‘placer’ is often one of the most laborious undertakings of the gold-digger. Pliny speaks of ‘the bringing of the rivers from the mountains, in many instances for a hundred miles, for the purpose of washing the _débris_,’ and this method of hydraulic mining is now carried on in California on a stupendous scale. Thus, north of Mariposa County, the thick deposits, often semi-indurated, are now washed down by vast streams of water (thrown by the pressure of a column of water of 150 feet), that do the work of running off the earth and gravel and gathering the gold in an incredibly short time. The ores of auriferous quartz are treated in a different way from the alluvial _débris_. After having been crushed and pulverised by powerful machinery, the finely powdered quartz is then treated with mercury, a method well known to the ancients. This metal dissolves out the gold, producing an amalgam, which, by straining and distillation, yields the gold.