640 OREGON AND NORTHERN CALIFORNIA. 
are frequent oscillations of forty-five degrees either side. Along 
Destruction River, at the encampment of October 7th, the rock dipped 
sixty degrees to the northeast. ‘The next day, while fording the river, 
the layers inclined sixty-five degrees to the northwest and north- 
northwest, varying from this to verticality. Still lower down the 
stream, the layers dipped from thirty-five to seventy degrees to the 
southeast and east-southeast, the smaller dip occurring alongside of a 
fissure four to ten inches wide, which was filled with fragments of the 
schistose rock ; receding from the fissure, the layers were curved, and 
the dip increased to seventy degrees in the course of thirty feet. 
Although we have no fossils to guide us to a knowledge of the age 
of this formation, yet its associations incline us to place it near the 
talcose and prasoid rocks, from whose material it 1s formed; and it is 
quite probable that a passage of the so-called Plutonic and metamor- 
phic rocks into beds obviously sedimentary or even fragmentary, is 
here exemplified. 
Basalt and other recent Igneous Rocks. 
Many a frosted peak stands to attest the former activity of volcanic 
fires in Oregon. Baker, Rainier, St. Helen’s, Hood, and others of the 
series, have been partially described. ‘These isolated cones so resem- 
ble the lofty summits of Mexico, that we cannot doubt, although 
they have not been ascended, that they once formed a line of vol- 
canoes through the whole extent of Oregon, and far into California. 
It is reported that St. Helen’s and Rainier have shown evidences of 
action within the three or four years past,* and an account is on record 
of ashes falling fifty years since. But these centres have not been the 
sole or even the principal sources of eruption. There are craters in 
the Coast Range, and others over the interior section. Mount Swa- 
lalahos south-southeast of Astoria is one of the former; several sum- 
mits beyond Fort Hall are among the latter; and many peaks may 
be added to the number when the country is fully explored. But 
besides these vents, there have been still wider eruptions from fis- 
sures over the country, near the peaks and subordinate to them as 
well as in more distant regions, and from this source extensive beds 
* Fremont mentions that on the 23d of November, 1842, ashes were ejected by St. 
Helen’s.—Rep. Exp. li. 1842, °43, 44, p. 193. 
