the South and Middle Yuba, California. 7 
The course of the ancient current where I had an opportutity 
of measuring it, appears to have been about 20°-25° west of 
north, (magnetic,) which it will be observed is nearly at right 
angles to the mean course of the middle and south forks of the 
Yuba; but it is not far from parallel with the axis of the Sac- 
ramento river valley, or of the great valley between the Coast 
Range and the Sierra Nevada. I have noted the same general 
direction of the scratches elsewhere in the great gold region, but 
additional observations are required to justify any comprehen- 
sive generalization. This much appears clearly shown, however, 
by the present state of our knowledge on this subject, viz: that 
the spread of the ancient gold-bearing gravel was produced by 
a cause greatly more elevated than the existing river system, 
or, which is more probable, at a time when the continent was 
less elevated than at present,’ and noving in a direction con- 
formable to the course of the valleys of the Sacramento and San 
Joaquim. We find it impossible to admit the existing river- 
system as a cause adequate to the spreading of such vast masses 
of rounded materials; the facts plainly point to a much greater 
volume of water than any*now flowing in the valley. The sec- 
tion already given illustrates perfectly the relations of the pres- 
ent river-system to the more ancient one whose grand effects are 
chronicled in the bed rock and its vast superincumbent mass of 
auriferous gravel. It serves also to illustrate the process now 
still in progress, by which the existing river system derived 
its gold-bearing sands, in great part at least, from the cutting 
away and secondary distribution of these ancient placers. 
Those who have had the opportunity of visiting other por- 
tions of the great gold region of California than that now 
under consideration will at once recognize the local characters 
of the details given as perfectly consistent with the general 
phenomena of the ancient placers as observed elsewhere; while 
at the same time great differences are found in many of the 
details. Thus in Calaveras and Tuolumne counties, 80 or 100 
miles farther south, the volcanic matter capping the auriferous 
gravel is found in the form of basaltic columns, beneath which 
recur the same phenomena already described. Here the wood 
contained in the gravel beds is beautifully agatised, or con- 
verted into semi-opal, as is the case also at Nevada City, Placer- 
ville, and elsewhere, associated with beautiful impressions ¢ 
leaves of plants and trees similar in appearance to those now 
found in this region. a 
? It is the opini i the larger of the erosion excavating the 
valleys of He cosaet ke tae thee the Tertiary venbed: It was probably 
ring this same time that the d plying auriferous gravel was produced from the 
degradation of the metamorphic schists and quartz veins of the Sierras by the joint 
action of water and of glaciers. a 
eed 
