among sedimentary rocks, lying in anything like a plain, even sheet of
equal thickness. On the contrary, it is seen to be marked by _folds_ or
plications, occurring at tolerably regular intervals, and crossing the
vein at an angle of 40° or 45° to the west. Similar folds may be
produced in a sheet which is hung on a line and then drawn at one of the
lower corners. The cross-section of the vein is thus made to resemble
somewhat the appearance of a chain of long links, the rolls or swells
alternating with plain spaces through its whole extent. Perhaps a better
comparison is that of ripples or gentle waves, as seen following each
other on the ebbtide in a still time, on the beach.

The distribution of the gold in the mass of the quartz appears to be
highly influenced by this peculiar wavy or folded structure. All the
miners are agreed in the statement that the gold abounds most at the
swells, or highest points of the waves of rock, and that the scarcely
less valuable mispickel appears to follow the same law. The spaces
between are not found to be so rich as these points of undulation; and
this structure must explain the signal contrast in thickness and
productiveness which is everywhere seen in sinking a shaft in this
district. As the cutting passes through one of these original swells,
the thickness of the vein at once increases, and again diminishes with
equal certainty as the work proceeds,--below this point destined again
to go through with similar alternations in its mass.

"There can be no fear, however," says Mr. Silliman, (Report, p. 10,)
"that there will be any failure in depth" (_i.e._, at an increased depth
of excavation) "on these veins, either in gold product or in strength.
The formation of the country is on too grand a scale, geologically, to
admit of a doubt on this point, so vital to mining success." Mr.
Campbell, whose masterly survey and analysis of the whole gold-region