630 OREGON AND NORTHERN CALIFORNIA. 
In the farther description of these rock-formations, we may take 
them up in the following order :— 
1. Ancient Plutonic rocks, or the granitic, hornblendic, and tal- 
cose. 
2. Early sandstone and conglomerate. 
3. Basalt, trachyte, and lavas. 
4. Tertiary formation. 
5. Alluvial deposits. 
ANCIENT PLUTONIC ROCKS. 
The various rocks included in this division are intimately asso- 
ciated with one another, and belong to a single series; and much that 
is interesting, geologically, is to be learnt from a study of their transi- 
tions and relations. ‘The granitic and talcose rocks are found to pass 
into one another through the hornblendic varieties, and the serpen- 
tine is one form of the rock in this gradation. 
Mineral Characters and Relations. 
Granitic Rocks.—The granite of the Shasty region is mostly albitic; 
it is very light coloured, and along the beds of streams, often has the 
whiteness of chalk. 
In the Shasty Mountains it is a fine-grained rock containing colour- 
less quartz along with the albite, besides scales of mica, which are black 
in the common variety, though occasionally silvery. At other locali- 
ties, the mica is wholly wanting, and the rock is a granular mixture 
of albite and quartz. Albite and feldspar were contained together in 
much of the rock, the former being easily distinguished by a flesh-red 
colour, while the latter is white. This feldspar is usually in coarse 
crystals, measuring sometimes half an inch by an inch and a half: this 
rock is, therefore, an albitic granite porphyritic with feldspar. 
True granite, containing no albite, occurs sparingly in the Shasty 
Mountains, and more abundantly near the Shasty River, where some 
of it is coarsely porphyritic, with but little mica and quartz. The 
mica of the rock is in wedge-shaped scales. 
These granites are handsome durable rocks, and have no trace of a 
schistose structure. A gneissoid variety passing into a gneissoid mica 
