228 The American Geologist. ^p"^' i^^^^- 
Here it is bounded on the east by the great hornblende schist 
fonnation and along its west border occurs a narrow belt of 
serpentine. 
The only remaining area of this formation known to me is 
developed in the vicinity of Yreka and Fort Jones in Siskiyon 
county where again it is associated with serpentine. 
The thickness of the Abrams mica schist in the upper 
Coffee Creek section is estimated at about i,ooo feet, but it 
seems to thicken to the southward and at Bully Choop may be 
much greater. 
This is undoubtedly a highly metamorphosed sedimentary. 
Originally it was a series of argillaceous sandstone beds in 
large part finely laminated. The action of the metamorphism 
has been to convert the nearly purely siliceous laminae into 
quartzyte layers, while folia of mica were developed in the shaly 
partings between the layers. In portions of the formation 
shearing such as usually produces schistosity has been nearly 
absent and the structure is rather that of a shale than a true 
schist. Yet this thermometamorphic action has been so in- 
tense that the original detrital granular nature of the material 
has been completely destroyed. Certain pure quartz sand 
layers have been converted into the apparent large quartz 
veins, which have a definite position in the series, are always 
parallel to the strike, and grade upward and downward into 
the distinctly laminated schist, yet rarely display the sub-gran- 
ular texture of a typical quartzyte. 
The Salmon hornblende schist. Whenever the boundary 
between the mica and hornblende schist has been examined 
by me, as in the south fork of Salmon River country and the 
Hay Fork section south of Trinity river, the former was found 
to grade into the latter through a thin series of graphite schist 
and actinolite schist. The black graphitic schist is particularly 
characteristic of this horizon and occurs nowhere else in the 
series. It was originally a highly carbonaceous layer in the 
succession of sandstones and shales and probably deposited un- 
der much the same conditions as veins of coal in the carbon- 
iferous rocks. The actinolite schist, so far as my observation 
goes, is also confined to this horizon. Usually it is of fine tex- 
ture, light green in color and has a peculiar bladed structure, 
but locally there is developed a coarse-textured type yielding 
