350 The American Geologist. June, 1904. 
be thought to be dikes in the slates. I have spent over six 
weeks at a point about six miles southeast of Hay Fork and 
have vigorously prospected along the contact between the vol- 
canic material and the shales, so that I believe the following 
statements are not mere guesses : 
The volcanic series in this region seems to be more basic 
than is usual in the vicinity of the Trinity and Sacramento 
rivers, and perhaps a large portion of it is altered basalt. There 
seems to be more lava and less tuff than farther east. Much 
of the lava is vesicular or amygdaloidal. There seems to be 
less alteration than is usual in the series. A representative suite 
of specimens from this area studied in the petrographical labor- 
atory along with as complete a set from the Clear Creek volcanic 
series of the area near Redding, I should expect to result in the 
•suggestion that they are not of the same age and do not repre- 
sent the same period of vulcanism. However, I map this west- 
ern area as Clear Creek because of its structural relations. 
The Bragdon formation southeast of Hay Fork village dif- 
fers from that of the eastern area in being finer in texture. 
The conglomerates farther east are here represented only by 
coarse sandstones, rarely becoming coarse enough to deserve 
to be termed fine conglomerates. They are composed of frag- 
ments of the same cherts as are the conglomerates of Trinity 
mountain. They occur often in heavy beds interstratified with 
the shales, and there is no unusual development of them at the 
base of the series. The shales are black and hard. They are 
very distinctly laminated and the bedding planes are quite 
evident at eveny outcrop. The same rate of decrease in thick- 
ness and texture of the Bragdon formation observed in the 
eastern area in going southwestward from its outcrop along 
the Sacramento river, if continued to the Hay Fork region, 
would produce precisely the characters which we find southeast 
of Hay Fork village. All the western belts I consider to have 
been deposited in the Bragdon body of water far from the 
the eastern shore and perhaps yet farther from any other 
shore. 
The volcanic series in a tributary of Dobbin gulch, about 
six miles southeast of Hay Fork was seen to rest on the 
cherty slates of the Paleozoic series. The basal stratum of 
the former seemed to be a lava sheet, in the lower portion 
