_Third_, They explain, also, why it is that, where streams flowing from one slope of a chain or ridge of mountains are found to yield rich returns to the gold-seekers, those which descend from the opposite slope often prove wholly unproductive. In the Ural, rich mines occur almost solely on the eastern, or Siberian slope of the great chain. On the western, or European slope, a few inconsiderable mines only are worked. So, as yet, in the Sierra Nevada in California, the chief treasures occur in the feeders of the Sacramento and San Joaquin rivers, which descend from its western side. The eastern slope, which falls towards the broad arid valley of the Mormons, is as yet unfamed, and may probably never prove rich in gold. These circumstances are accounted for by the fact that, in the Ural, the older rocks, of which we have spoken as being especially gold-bearing, form the eastern slope of the ridge only, the western flank of the range being covered for the most part by rocks of a more modern epoch. The same may be the case also with the Sierra Nevada where it is still unexplored; and the Utah Lake, though remote, by its saltness lends probability to this conjecture. _Fourth_, and lastly, they make clear the distinction between the “dry and wet diggins” we read of in our Californian news—why in so many countries the beds of rivers have been deserted by the gold-finders, and why the river banks, and even distant dry and elevated spots, have proved more productive than the channel itself.[8] Let us attempt to realise for a moment the condition of a country like California, at the period, not geologically remote, when the gold-bearing drift was spread over its magnificent valley. The whole region was covered by the sea to an unknown depth. The snowy ridge, (Nevada,) and probably the coast ridge, also formed lines of rocky islands or peaks, which withstood the fury of the waves, and, if they were covered with ice, the wearing and degrading action also of the moving glaciers. The spoils of the crumbling rocks sank into the waters, and were distributed by tides and currents along the bottom of the valley. The narrow opening through the coast chain, by which the bay of San Francisco now communicates with the Northern Pacific, would, at the period we speak of, prevent the debris of the Nevada rocks from being washed out into the main basin of the Pacific, and this would enable the metallic, as well as the other spoils of these rocks, to accumulate in the bottom, and along the slopes of what is now the valley of California.