It is also found in the form of rolled lumps and grains, "stream tin," in alluvial gravels; the latter are secondary deposits, the products of the disintegration of the first-named primary deposits.
Permeability is practically identical with the speed at which percolation takes place; through clay it is slow, but increases in rapidity through marls, loams, limestones, chalks, coarse gravels and fine sands, reaching a maximum in soil saturated with moisture.
The " pan " is now only used by prospectors, while the " cradle " and " tom " are practically confined to the Chinese; the sluice is considered to be the best contrivance for washing gold gravels.
Even the Calaveras man is no exception, since his skull and his polished conical pestle, the latter made of stone more recent than the auriferous gravels, show him to have been of Digger Indian type.
In North America the sites have been examined by the Peabody Museum, the Bureau of American Ethnology, and others, with the result that only the Trenton gravels have any standing.
