674 OREGON AND NORTHERN CALIFORNIA. 
the course of its changes resisted removal in any part, the part left 
standing would form a subordinate terrace between the upper level, 
or that of the plain before the rise began, and the lower level, or that 
attained when the elevation ceased. 
If this be a true statement of the effects, a terrace slope might be 
formed by a gradual elevation; and also without any intermission in 
the process, there might be intermediate terraces in some parts of the 
same region. We cannot therefore consider a terrace in an alluvial 
region certain evidence of an abrupt rise of the country,—or, what is 
the same in its results, an abrupt sinking of the sea level. 
We may hope that at some future period, the observations on 
terraces east of the Rocky Mountains will enable us to give the whole 
throughout the Continent a general survey. They point to a grand 
geological phenomenon, in which a continent was concerned; and, if 
properly studied, they must throw new light on the great geological 
changes that have been in progress throughout the globe. 
Boulders at Wallawalla.—The plains about Wallawalla, within two 
miles of the river, are covered with granite boulders, some of which 
are six feet in diameter. ‘The whole region around is basaltic, and 
the nearest granite occurs seventy miles up the north fork of the 
Columbia. Granite is also found in place on the south fork of the 
Kooskooski. 
The submerged forest in the Columbia above the Cascades has 
been supposed to indicate a change of level; but it is referred with 
more reason to slides from the banks of the stream, occasioned by the 
undermining action of the water. It extends up the river at inter- 
vals for five miles, and the trees stand erect, apparently as they grew; 
the stumps project above water when it is low. ‘The wood is soft and 
rotten without being at all petrified. 
The Grande Coulée, cutting across the great bend below Fort Col- 
ville, is another evidence of change at some former period. ‘There 
can be but two ways by which valleys can originate in a country of 
horizontal rocks, (indicating, therefore, no upturning, )—one by denuda- 
tion, the other by rupture and subsidence. The question with regard 
to the origin of this gorge is therefore narrowed down to a decision 
between the two. The fact that some of the granite hills in the gorge 
are capped with basalt at the same height as the basaltic layers of the 
sides, sets aside the idea of subsidence; for we cannot assume a sub- 
sidence of a large area to have taken place, and leave at the same time 
