48 THE ROYAL SOCIETY OF CANADA 
t is hoped that it may be possible to compare these two runs of gold 
more fully at some future time. 
If the erosion of a valley were to continue downwards uninter- 
ruptedly in rock of similar character throughout until its bottom should 
have reached base level before the stream which formed it began to erode 
laterally, the gold would be distributed in a continuous line along the 
bottom of such a valley and when the stream had afterwards widened 
it and had formed alluvial flats and flood-plains the pay-streak would 
be continuous through and under these alluvial flats. 
But streams rarely, if ever, deepen their channels uninterruptedly 
in this way. Harder bands of rock cause obstructions, and elevations 
and depressions of the land cause the water to flow with different veloc- 
ities at different times, so that at one time, or in one part of its channel, 
a stream may be cutting into the bottom of its valley, while at another 
time and in another part of its channel it may be filling it up and cover- 
ing it with alluvial sand and gravel. 
In this way a stream with a valley of any considerable depth has 
probably formed a number of flood-plains at different periods in its 
history, and remains of these flood-plains may often be seen as terraces 
on the sides of its valley. 
When a stream has formed a flood plain the pay-streak will, as we 
have seen, run beneath that flood plain on a line marking the original 
bottom of the old V-shaped valley and if, when the stream again begins 
to cut through this flood plain and into the rock beneath it, it follows 
the line of the former stream, or, in other words, if it follows the line of 
the pay-streak, it carries the pay-streak down with it; but if it diverges 
from this line, a portion of the pay-streak remains on the terrace. If 
it continues to deepen its channel until all the terrace is removed, or at 
least until that portion of it is removed which contains the pay-streak, 
the gold will also all be in the pay-streak in the bottom of the new 
valley, but if it reaches a new base level before the pay-streak is all re- 
moved from the terrace a new condition is introduced. The stream 
may begin to cut into the side of its valley and may cut into and remove 
the old terrace containing a portion of the old pay-streak. In that case, 
the gold may drop down into the bottom of the valley with the eroded 
rock and gravel and form a rich pocket at one side of, and often quite off 
the line of the original pay-streak or it may be distributed along the 
channel which the stream happens to be following at the time. If the 
renewed stream happens to cut into the old valley bottom to one side of 
the original pay-streak, or across it at several places and to diverge from 
it at a number of other places, the new pay-streak may be weak and 
indefinite, or it may be rich in spots and very poor between those spots, 
with other rich spots to one side or the other. In fact, it may assume 
