GEOLOGY OF CENTRAL WASHINGTON TERRITORY. 483 
The upper Columbia and its tributaries, through the whole route of the expedition, presented 
this formation upon a scale of singular magnitude and variety of circumstance. It is probable 
that in this northern district, where the winters are exceedingly cold, ice has played an import- 
ant part upon these elevated lakes; but the surface of the country exhibits no evidence of its 
action subsequent to their drainage, and there are no appearances either of the former existence 
of fixed glaciers, or the transportation of boulders from a distance by moving bodies. In fact, 
rocks out of place are of very rare occurrence, considering the mountainous character of the 
country, and nowhere to a size or extent beyond the capacity of ordinary causes. 
On leaving the Columbia to visit the Chelan lake, our route ascended one of these terraces, 
rising to the height of six hundred and forty feet in a single slope, and occupying a recess in the 
hills which bordered it. On reaching the top, it proved to be the entrance of a level valley, 
extending through the hills and emerging at about one hundred and fifty feet above the lake. 
This valley or coulée is only one of a number noticed in this region, and is analogous to the 
“cots” or ‘land straits” described by Sir Charles Lyell, (Manuel El. Geol., ch. vii.) The lake 
is four hundred and seventy-four feet above the Columbia at its mouth, and its outlet makes this 
descent in about four miles. It did not appear to be very deep, though it occupies a narrow 
valley between precipitous mountains of syenite; the detritus of these having probably filled it up. 
Its length seems, from Indian account, to be thirty-five or forty miles. It affords a good illustra- 
tion of what the other terraced valleys formerly were; the appearance of its shores indicating 
that, should the barrier at its mouth be removed, similar terraces would remain to those which 
border the Columbia at its mouth. 
The most remarkable exhibition of these is, however, upon the Methow river—the barrier R. 
of Wilkes’s map. In crossing the mountains between Fort Okinakane and that stream, we 
noticed, upon the summit and high up on the sides, remains of those formed previous to their 
elevation; but the valley of the river itself is lmed with others of a later date. According to two 
or three of the barometrical observations taken in surveying the supposed pass, the altitudes of 
these appear to agree sufficiently with some on the Columbia to indicate their connexion. In 
descending the river, we met with two dams or barriers which had once restrained its waters, 
and concerning which there could be no question. The first was externally a mere well of 
detritus, though probably with a rocky foundation. It was level on the top, and sloped at the 
sides like the lateral terraces. Half a mile below was the second, which was formed against a 
protruding point of rocks. In both cases the river had cut merely a narrow channel through 
them on one side, leaving the rest standing. The walls of syenite on the Methow were in many 
places cut and smoothed by the action of the water at a height of seventy-five or eighty feet 
above its present bed. At the mouth of the river no less than eighteen terraces, rising one above 
another, were counted. Small moraines were noticed in this valley, but apparently rather the 
result of violent rush of water from lateral branches than of ice. The valley of the Methow 
affords a richer field for the geologist in plutonic and metamorphic rocks than any other portion 
of the Territory visited by the survey, and would richly reward a careful exploration. Gneiss, 
syenite, and granite occur, well characterized and blended with each other. The syenite is 
often divided by joints so as almost to appear stratified, and to give its perpendicular walls 
the semblance of artificial construction. The gneiss is found both horizontal and displaced by 
the intrusion of trap. Associated with these are also serpentine conglomerates and prophyry. 
Almost all these rocks pass by insensible gradations into one another, and their relative positions 
are excessively complicated. There appears to be a very great resemblance between the 
geology of this part of the Cascades and that of the Shasta mountains, as described by Wilkes 
in his memoir on Western America. 
The rock in place on the Columbia between the Chelan and the mouth of the Okinakane 
was syenite, varying somewhat in character. It was frequently intersected with large veins of 
feldspar. In crossing from Fort Okinakane to the forks of the Methow the syenite changed to 
