632 OREGON AND NORTHERN CALIFORNIA. 
waters of the Sacramento,) in the Shasty Mountains. It occurs of 
various shades of gray, green, and brown, and the worn masses appear 
spangled with the pearly crystallization of the light grayish-green 
hypersthene. Hypersthene and hornblende are different varieties of 
the same mineral, the former having a pearly or submetallic lustre. 
Talcose Rocks and associated Silceous Rocks.—The talcose rocks of 
this region have seldom the usual schistose structure; they are gene- 
rally compact, and irregularly fissured like the hornblendic rock above 
described. ‘These compact varieties contain little talc, or graduate 
into a siliceous homogeneous rock, breaking with a smooth surface, 
consisting probably, for the most part, of silica and feldspar, or of 
silica alone, excepting some included clay. 
A fissile variety having imperfectly the lustre of tale occurs in some 
of the ridges of the Umpqua Range; it is a grayish-green or grayish- 
white rock, too fragile and soft to break out in slabs. It occurs along 
with the hard compact rock alluded to. This compact rock has a 
grayish or olive-green or brownish colour, with none of the greasy feel 
of talc, and breaks into angular fragments, four or five inches through. 
No trace of crystallization could be distinguished, except in the quartz 
veins which thickly intersect it. It contains little or no talc, except- 
ing as colouring material, and it is possible that the colour may be 
owing to a trace of hornblende. Other portions of the same rock are 
nearly pure silica. 
In the Shasty Mountains there is a talcose slate of a dark grayish-black 
colour, breaking into thin slates with a fine surface, and but slightly 
greasy in feel. This slate graduates into a compact rock resembling 
that just described. The colours of the latter, besides those stated, 
are often light bluish-green and greenish-white or grayish-green ; and 
when forming the bed of a river, the waters have consequently the same 
mellow tint. Veins of milky quartz are common. This greenish rock 
would be called prase in hand specimens, and is often more or less 
translucent, with a smooth conchoidal fracture. It is very siliceous, 
consisting probably of silica and feldspar, with a trace of colouring 
material, yet the feldspar is nowhere in crystals or grains, and in much 
of the rock must be sparingly present. We may distinguish it as 
prasoid rock, for it is abundant wherever the talcose formation occurs. 
Fragments of handsome prase are occasionally met with in these re- 
gions, which have sometimes the oily surface of talc. 
A light greenish variety of this rock, near San Francisco, is associ- 
ated with red and yellow jasper ; some hills consist wholly of the latter 
