bussell.] TERTIARY FORMATIONS. 61 
rocks are usually dark yellow, but occasionally, as near Narrows, are 
nearly white, and in some instances are sufficiently compact to be 
used for building stone. Associated with the layers of consolidated 
pebbles and sand just referred to, and having a wide extent in both 
Idaho and Oregon, are soft unconsolidated light-colored shales and 
marls -and thick beds of nearly white sand and light-colored clay. 
Beds of this general nature aggregating more than a thousand feet 
in thickness underlie the Snake River between Glenns Ferry and 
Weiser and form the conspicuous white bluff along each side of that 
stream. Similar beds occur also in the lower portion of the valley of 
Malheur River and beneath the rim rocks of the canyons on the west 
slope of Stein Mountain. Light-colored and in part greenish shales 
outcrop on the west side of Alvord Valley, where they pass beneath 
the sheets of basalt, forming the bold eastern face of Stein Mountain. 
Fine exposures of rain-sculptured lacustral sediments, usually of a 
peculiar light-greenish tint, occur on the border of Owyhee River, 
near the mouth of Jordan Creek (PL XVIII). Similar beds are 
present also in the mountains of Owj^hee County, Idaho, and are a 
southward extension of the thick sediments exposed along Snake 
River. This same formation extends northward from Snake River 
and is exposed near Boise and in the valley of Payette River. From 
its abundant exposures along the last-named stream it has been 
named by Waldemar Lindgren the Payette formation. 
While the Payette formation has a wide extent in Oregon, and pos- 
sibly reaches to the John Day River, where other similar beds outcrop 
and have been independently named, it is not positive that all the 
exposures of similar material as far south as Harney and Silver lakes 
were deposited in the same lake basin. . The lacustral sediments 
beneath the basalt of Stein Mountain reveal a thickness of fully 
1,000 feet, and, as seems probable, are of older date than the Payette 
formation. 
Interbedded with the sandstone and shale, of the formations just 
mentioned, and frequently forming a considerable and at times 
seemingly the major part of their thicknesses, are beds of exceedingly 
fine white volcanic dust. This dust was blown out of volcanoes 
while in a state of violent eruption, and, falling in lakes, or being 
washed into them by streams, became interbedded with other sedi- 
ments or intimately commingled with them. Examples of pure 
white volcanic dust from 10 to 20 or more feet thick may be seen 
in the hills on the lower course of Owyhee River, a few miles south of 
Owyhee, and are also splendidly exposed near Beulah (PI. XVII). 
Outcrops of material of the same nature, conspicuous on account of 
their whiteness, occur beneath the rim rock near Diamond, in the 
borders of the small valleys in the northern portion of Owyhee 
County, Idaho, as well as at a large number of localities in the bluffs 
bordering Snake River. 
