652 OREGON AND NORTHERN CALIFORNIA. 
coast section of Oregon. It characterizes many of the hills and plains 
along the Straits of De Fuca, the Cowlitz, the Lower Columbia, the 
Willammet Valley, and the Elk; and although interrupted by more 
ancient rocks between the Umpqua, (on the route to California,) and 
the Boundary Range, it appeared again in this range, and continued 
nearly to the Shasty Mountains ; here commenced a second interrup- 
tion by the older rocks, and we found the tertiary again only on the 
San Francisco Bay, near its head. How far the same deposits extend 
toward the interior, we had no satisfactory means of ascertaining. 
On the Columbia banks, it is replaced by basalt above twenty-five 
miles from the sea; but the country either side is still character- 
ized by sandstone or shale, with intermingled basaltic hills. High 
up, at the Cascades, and beyond for some distance, there are basaltic 
conglomerates, believed to be of the same age. Some vegetable im- 
pressions from Fraser’s River, imbedded in a blue shale, (fig. 10, plate 
21,) belong apparently to this formation. 
The thickness of the formation on the Columbia and Willammet, is 
in many places, a thousand or twelve hundred feet. We ascended 
twelve or fifteen hundred feet of the sandstone, in the Elk Mountains; 
for fragments at top, and exposed horizontal layers at the southern foot, 
indicated that the whole was sandstone. Killimook Head, on the 
coast just south of the Columbia, consists of clayey layers alone, and 
is nine hundred feet in height. As in both of these instances the 
rocks had evidently been much removed by denudation, it 1s probable 
that fifteen hundred feet is even too low an estimate for the whole 
height above the present sea level. 
Inthological Characters.—The rocks of the formation are soft sand- 
stones, more or less argillaceous and schistose, and clay shales, either 
firm or crumbling, besides basaltic tufa or conglomerate. 
The sandstone consists generally of granitic material, though some- 
times of basaltic. In the former case, (as it occurs on both sides of 
the Columbia east of Astoria,) the constituents of granite,—feldspar, 
quartz and mica,—are readily distinguished, and especially the mica, 
in silvery scales. The rock has a sandy colour, and is usually brittle, 
or even friable; yet some deposits afford a firm and durable building- 
stone. 
As the rock becomes argillaceous, the sandstone assumes a lami- 
nated structure, exhibiting each successive layer of deposition ; and 
these lamin are generally less than an eighth of an inch thick. The 
laminated variety of sandstone is, perhaps, more common than the 
