GRANITIC AND ASSOCIATED ROCKS. 635 
eranite may be detected receiving at first a mere sprinkling of horn- 
blende points among the scales of mica. These pass into syenites, 
and the syenites into hypersthene rock, and into a compact horn- 
blendic rock which has no trace of crystallization. The passage to 
talcose rocks is equally distinct and gradual. Both the granitic and 
hornblende rocks become, at times, very gradually talcose, so that it is 
often difficult to say whether the rock should be classed with the talcose 
series or not. The talcose rocks graduate as imperceptibly into the 
prase rock, in which the tale is nearly or wholly wanting; and this 
again into the red and yellow jaspers. ‘The transition to serpentine 
from the hornblendic and talcose rocks has been mentioned. The 
diallage of the serpentine is nothing but hornblende, and seems to cor- 
respond to the hornblende crystals in the syenite. ‘The mineral horn- 
blende is common in most serpentine rocks, either as asbestus, actino- 
lite or diallage. We have described an imperfect serpentine in the tale 
near San Francisco, and mentioned that actinolite occurs abundantly at 
the same locality ; indeed the serpentine at this place appears to owe its 
hardness to an excess of hornblende in its composition. At the same 
localities, the green and red cherts or jasper occur along with the tal- 
cose slates. 
Topographical Relations.—The various rocks under consideration 
have appeared to follow some kind of system or regularity in their 
associations with one another. 
The talcose formation was first met with, travelling south from the 
Umpqua; next we came upon syenite, then true granite upon the 
Shasty River. Leaving our southerly course, and travelling eastward 
on the Shasty, we passed again to the hornblende rocks, syenitic and 
compact. Returning to our southerly course, after twenty-five miles, 
we again fell in with granitic rocks, at first passing over gneiss, and 
soon after, granulite and some true granite. The granite continued to 
the Boundary Range, where it was syenitic. 
After passing a region of basalt and sandstone in the vicinity of the 
Clammat, we crossed a prairie covered in many parts with pebbles 
from the talcose formation ; then the foot of a ridge of serpentine ; and 
then entered into a region of syenite at the foot of the Shasty Moun- 
tains. For twenty miles in these mountains, these rocks were inter- 
rupted by trachytes; yet a few pebbles or stones from the talcose 
formation were found in the narrow beds of small mountain streams. 
Leaving the trachyte, boulders of talcose rock and syenite occurred 
abundantly along the head waters of the Sacramento, and within a 
