By mere washing with water, it is impossible to extract the finer particles and scales of gold either from the natural sand or from the pounded rock. But an admixture and agitation with quicksilver licks up and dissolves every shining speck, and carries it, with the fluid metal, to the bottom of the vessel. The amalgam, as it is called, of gold and quicksilver thus obtained, when distilled in a close vessel, yields up its quicksilver again with little loss, and leaves the pure gold behind. For the perfect extraction of the gold, therefore, from its ores, quicksilver is absolutely necessary, and it can be performed most cheaply where the latter metal is cheapest and most abundant. Hence the mineral conditions of California seem specially fitted to make it an exception to all gold countries heretofore investigated, or of which we have any detailed accounts. They promise it the ability to supply a large export of gold, probably long after the remunerative freshness of the diggings, properly so called, whether wet or dry, shall have been worn off. But both the actual yearly produce of gold, and the probable permanence of the supply, have been greatly increased by the still more recent discoveries in Australia. A wider field has been opened up here for speculation and adventure than North-Western America in its best days ever presented. We have already adverted to the circumstances which preceded and attended the discovery of gold in this country, and new research seems daily to add to the number of districts over which the precious metal is spread. It is impossible, however, even to guess over how much of this vast country the gold field may extend, and of richness enough to make washing possible and profitable. The basin of the river Murray, in the feeders of which gold has been found in very many places, has a mean length from north to south of 1400 miles, and a breadth of 400—comprising an area of from 500,000 to 600,000 square miles. This is four times the area of California, and five times that of the British Islands; but whether the gold is generally diffused over this wide area, or whether it is confined to particular and limited localities, there has not as yet been time to ascertain.