354 ^/'^ American Geologist. June, 1904. 
sives which are known to be post- Jurassic in age, there will 
remain in the very cherty belt, innumerable diabasic and dior- 
itic dikes which are usually small. In the known Carbonifer- 
ous belt, similar material occurs in much larger bodies. This 
may mean little, but it helps one to distinguish this belt. I be- 
lieve I have crossed these Upper Carboniferous rocks near the 
mouth of Salmon river in line with the formation as it is de- 
veloped at Patterson's, but the broad belt east of it I consider 
as most probably Devonian in age. The structure then will be 
that of a syncline. Near the center are the newest rocks, the 
Bragdon formation of probable Jurassic age. This is bordered 
by Triassic volcanic rocks. Next on the east come Upper Car- 
boniferous rocks, and perhaps a corresponding belt may be on 
the west. Farther out on both sides we seem to have Devonian 
rocks and these followed by pre-Devonian schists. 
The total absence from aH of the western Bragilon areas of 
intruded igneous material such as everywhere abounds in the 
known Paleozoic areas must be significant. To place this 
Bragdon series in the Upper Carboniferous or any older period, 
one must assume that the dike material exercised a remarkable 
selection. My interpretation is that after the Paleozoic series 
was completed, the dikes were injected into it during the Trias- 
sic period and that portion of the igneous material which 
reached the surface became the lavas and tuffs of the Clear 
Creek volcanic series. Clear Creek areas occur in the supposed 
Devonian polt east of the known Upper Carboniferous belt and 
are clearly non-conformable to the Paleozoic rocks. Presently 
the vulcanism ceased, the volcanic land was eroded, then sub- 
merged and the Bragdon formation laid dotvn. We have in 
these western areas the same stratigraphic relations as in the 
eastern Bragdon area. 
THE AGE OF TILE BR.\GDON FORMATIOX. 
In the vicinity of Delta, on the Sacramento river, the pre- 
Bragdon erosion of the volcanic scries seems to have proceeded 
to the extent of cutting it through in many places and making 
it discontinuous. This enables the Bragdon formation to come 
down on to the Paleozoic rocks. Last summer, while following 
the Little Dog creek trail and again the trail on the line of the 
new wagon road between Delta and Trinity Center, I noted, 
with surprise, small areas of silicious shales like the Paleozoic, 
