TERTIARY FORMATION. 653 
compact. The colour is often quite light, from the white clay that is 
combined with the sand. 
With still more clay, the rock is a slate or a crumbling shale. The 
shale rock often appears like a bank of clay, and is so slightly com- 
pacted that a mere touch of the hammer crumbles large masses to 
pieces. Its colours, besides those of the sandstone, are often dark blue, 
dull green, brown, and blue-black; and the last is one of the most 
common. Some of the firm shales of this dark colour, could not be 
distinguished in their characters from the older secondary or silurian 
deposits. At Killimook Head, south of the mouth of the Columbia, 
the cliff, nine hundred feet high, (as ascertained by Mr. Drayton,) con- 
sists, for the lower two-thirds of its height, of a dark-blue clay rock, 
somewhat slaty. Above this the clay has a white colour, and so much 
resembles chalk as to have been thus called by the settlers. 
The compact sandstones are in general very irregular in the extent 
and thickness of the layers. Layers apparently distinct at one place 
are coalesced at another place near by, and again they become sub- 
divided, as in the Sydney sandstone, New South Wales, (page 462.) 
Thin layers of clay or clay shale often intervene, which disappear after 
running on for a short distance. Besides the interpolated beds of 
clay, there are also fragments or small masses of clay imbedded in the 
compact rock, and in some parts the clay thickly mottles the sand- 
stone. 
The shales appear in some cases to be largely developed in the 
lower part of this formation, while the upper layers consist mostly 
of sandstone. ‘This was found to be the fact at Elk River, where 
hills of sandstone four or five hundred feet high overlie the shale. 
On the Columbia, the two rocks were seldom seen closely associated. 
The shales are in general most abundant on the south side of the 
river, and the sandstones on the north. At the west cape of Gray’s 
Bay, the lowest layer is shale. We cannot say from our own observa- 
tions whether the shale will prove to be generally the lowermost of 
the series. 
The basaltic conglomerate and sand-rock vary much in texture, but 
the finer varieties are usually of a dirty ochreous colour. They 
occur in the Willammet Valley, about fifty miles north of the Elk 
Mountains, forming hills and underlying the plains, and also in the 
Boundary Range and the adjoining country. In these regions, the 
transitions to the granitic tertiary sandstone may be distinctly ob- 
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