52 
GEOLOGY-MARL HILLS-MOUNDS. 
the north are long and gentle—toward the south, short and steep. The view from their sum¬ 
mits is exceedingly picturesque and peculiar. Except on the slopes of the Cascades, no forests 
are visible. Lines of trees follow the streams which come down from the mountains far out 
into the prairies, and a few pines and cedars crown the summits of the hills lying southward. 
With these exceptions, the whole country is covered by a sparse growth of grass, now every¬ 
where dry, tinging the landscape with a universal monotonous brown. 
The Cascades, from this point, exhibit a scene of unusual grandeur. Mount Hood, directly 
west, rises to a height, variously estimated, at from 15,000 to 18,000 feet; its summit not unfre- 
quently enveloped in clouds, and, in a clear atmosphere, giving off steam or smoke. Mount 
Jefferson distinctly visible in the west, and Mount Eainier and Mount Adams, snow peaks north 
of the Columbia, in the northwest. The canon of the Des Chutes appears like a deep, dark 
gorge, traversing the plateau of which I have spoken. 
The region lying between the Tysch mountains and the Columbia is occupied by a series of 
rounded grass-covered hills, having an altitude above the valleys which divide them of several 
hundred feet ; precisely resembling, in appearance, the sandstone hills about Benicia, in Cali¬ 
fornia. They are composed of white, frequently infusorial, marls, belonging to the same series 
with those which cover so large a surface in other parts of the Des Chutes basin. Here, as 
elsewhere, the infusorial forms which they contain are of fresh water origin. 
Mounds .—Every day while traversing the Des Chutes basin we noticed upon surfaces unoc¬ 
cupied by trees numbers of low and rounded mounds, apparently formed by causes not now in 
operation. As we progressed toward the north, they became more numerous and of larger size. 
In the vicinity of the Dalles they form a very marked feature in the scenery ; in many places 
covering the prairies and hillsides so completely that their margins are almost in contact. They 
have here an altitude of from three to five feet, and a diameter of from twenty to fifty. Although 
I have examined them with great care, I have been unable to arrive at any satisfactory conclu¬ 
sion in respect to their origin. They occupy equally the hillsides and the levels, and exhibit 
no traces of stratification, nor is there anything in their structure which afforded me any clue 
to the cause or manner of their formation. I have seen in California mounds not very unlike, 
but of less magnitude, formed by burrowing squirrels, but it seems impossible that this cause 
could have here produced them. 
