GEOLOGY-STRIPED SANDSTONE —TYSCH MOUNTAINS. 
51 
due to the regularity of their outlines, as well as to the entire absence of recent volcanic rock. 
The slates which for the most part compose them are’ alumino-silicious, very hard and highly 
metamorphosed, exhibiting the same general characters with those which form so prominent a 
feature in the geology of the Cascade mountains west of its principal axis. They are divided 
by deep, narrow ravines, and their slopes are long and steep, generally unbroken by any project¬ 
ing crag or perpendicular wall. The surface of these mountains is in many places strewed 
with geodes and crystals of quartz, or masses of chalcedony, which -have apparently filled 
cavities in the rocks composing them. 
At Nee-nee Springs, several miles north of the Warn Chuck valley, stratified tufas—here 
somewhat disturbed and broken—exhibit varieties of metamorphism not before noticed. What 
was formerly one of the finer marls is here converted into a kind of fine-grained sandstone, 
marked with ribbon-like lines of red and white. These seem to be the lines of deposition, and 
indicate a periodical recurrence of the effects produced by two sets of causes. The red lines, 
which are perfectly distinct—sometimes not thicker than a sheet of paper ; more frequently 
combining to form bands a quarter of an inch in width—alternate with lines of white of about the 
same width and of somewhat coarser texture. Small masses of scoria are disseminated through 
the rock, and over these the lines of deposition are flexed, showing that the different bands 
were formed by alternating layers of sediment—the flexures of the lines of deposition over a 
foreign body indicating, even in a hand specimen, which was the superior and which the 
inferior surface. The general parallelism, and the continuity of the most delicate lines of 
color, show that these sediments were deposited in tranquil water—the bands of red indicating 
the periods of most perfect quiet, when the finer materials, including a larger quantity of iron, 
sank to the bottom. I have supposed it possible that the presence of iron in the red bands was 
due to infusoria. If this material were carried through the same stages of metamorphosis 
as much we have seen, it would form beautiful ribbon jasper. More perfect imitations of the 
ribbon jasper of Germany and Egypt were, however, found at the Hot Springs, where a jaspery 
rock was marked by bands of red and green. 
TYSCH PRAIRIE. 
North of the Warn Chuck mountains we came down on to Tysch prairie, which forms 
a plateau precisely similar, in all its general features, to those we had previously traversed, 
but lying at a lower level, having an altitude of but 2,200 feet above the sea. Mount Hood 
rises from its western border, presenting an appearance remarkably imposing and beautiful, 
well represented in plate No. IX, illustrating the general report of Lieutenant Abbot. From 
the base of the Cascades it stretches eastward for thirty miles or more, forming a nearly level 
plain, cut by the deep canons of Tysch creek and the Des Chutes. This plain is everywhere 
underlaid by a stratum of trap, beneath which is a series of stratified tufas. 
TYSCH MOUNTAINS. 
The mountains which bound Tysch prairie on the north rise to an altitude of about 2,500 feet 
above it. Their outlines are all rounded, and they are composed principally of compact trap, 
not of recent date; and of which all the rough and ragged surfaces have been worn away by 
the action of the elements. 
Like Warn Chuck mountains, rising abruptly from the plateau which surrounds them, they 
have a peculiar insular appearance. Like the Warn Chuck mountains, too, their slopes toward 
