82 The America?i Geologist. February, 1900 
the contact from one level to another, we find the hornblende 
schist in place next the serpentine near the summit of the 
ridges and peaks, while at lower levels, the graphitic and 
chloritic schists adjoin the serpentine, and finally the mica 
schist forms one wall of the contact. Toward the south, all the 
formations rise, and where the fault crosses the head of Swift 
creek, the walls are both of serpentine at lower levels, with a 
sharp wedge of mica schist on the west of the contact at higher 
levels. Along the ten miles that I have traced this eastern or 
Keating fault, the displacement of the strata amounts to be- 
tween 1,000 and 2,000 feet, with upthrow always on the east. 
The western or Laivrence Fault occurs about one-half mile 
west of the other^ is parallel with it, and is very similar in 
geologic features. Throughout its course, as traced, of over 
ten miles, it displays an upthrow on the east of between 1,000 
and 2,000 feet, the eastern wall of the contact being serpentine 
at lower and middle levels, and north of Pin creek mica schist 
at the higher altitudes. On the west are the mica and horn- 
blende schists ; these, at some distance from the fault, have a 
normal dip westward toward the Carboniferous schistose slates 
of the Salmon river country, but near the fault, they are re- 
versed, dipping steeply eastward, and hence cut off at a high 
angle by the break in the strata. 
Generalizing the preceding, we may say that the long west- 
ward normal slope of the strata in the Upper Cofifee creek re- 
gion is interrupted by two long breaks or faults, the block of 
strata between which has been compressed and tilted eastward 
so as to reverse the normal dip of the strata. This was one 
phase of the same mountain-building action which produced 
the great folds, and its age may be referred to a time between 
the close of the Jurassic and the latter part of the Cretaceous 
period. 
hitrusives. 
The territory of the Sierra Costa mountains is characterized 
by remarkably diverse systems of massifs and dikes of igneous 
or trappean rocks. The series comprises nvunerous repre- 
sentatives of at least eight distinct intrusions of granitic, dior- 
itic and diabasic material. The remarkable feature of their 
occurrence is that although so radically different in composi- 
