175 
THE NORTHERN PACIFIC ROUTE. 
so that in case of an oversupply of one they will have another to fall 
back upon. 
The volcanic rocks that border the Naches Valley and extend within 
a few miles of North Yakima furnish an interesting example of a 
recent lava, flow. The hummocky surface of this plateau between 
Naches River and Cowiche Creek, although in places covered by sage- 
brush and bunch grass, exhibits the essential features of a cooling lava 
flow, and at many points on its borders the characteristic jointing 
due to contraction on cooling is shown in rare perfection. (See Pl. 
North of North Yakima the railway crosses Naches River and then 
passes through Yakima Ridge in a short canyon cut in the thick layers 
of basalt, which have here, as in the other ridges to the south, been 
folded into a low anticline.’ 
1 After having traveled up Yakima 
River for nearl miles and passed 
through a number of basalt ridges, the 
traveler may be surprised at the apparent 
disregard of the stream for the ridges and 
valleys. As stated previously, the prin- 
cipal arches and troughs into which the 
ave been bent trend in a nearly 
_ nari and if the streams fol- 
ourses they would encoun- 
a little difficulty, j in reaching their des- 
tinations. But instead of following the 
of its course no less than seven ridges of 
arched or upturned basalt. What made 
the stream select its present course, and 
why did it persist in this course across the 
arches of hard rock when it might have 
found an outlet to the Columbia on the, 
east by an open synclinal valley? 
In order to answer this question it will 
the lake was filled or there was an uplift 
e region which changed it to a land 
Columbia rivers were formed, before the 
great in the rocks had been pro- 
duced. After the streams were well es- 
tablished, in about the same courses that 
they follow to-day, a great north-south 
pressure wrinkled the rocks into a series 
of broad, shallow troughs and rather short 
arches. Many persons think of such a 
movement as having occurred suddenly 
and as having crumpled the rocky layers 
as leaves of paper may be crumpled in the 
hand. Ii the movement had been sud- 
den, then the southward-flowing stream 
would have been dammed wherever one 
of the arches crossed its pathway, and 
Yakima River, instead of flowing as it 
does to-day, would have been broken into 
a number of separate streams, each 
which would probably have found an out- 
let to the east into Columbia River. 
this did not happen, it seems evident that 
the movement was not rapid, but was so 
slow that the stream cut the rock away as 
fast as it was forced up. As the down- 
ward cutting of a stream in hard rocks is 
done very slowly, it follows that the arch- 
ing of the strata must also have been a 
very slow process, probably occupying 
thousands of years. Although the move- 
ment was slow, it sear ual nine of 
non a 
or 
zk 
til! 
LL yy 
through 
structure or topography of the region. 
