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GRANITIC AND ASSOCIATED ROCKS. 637 
very distinct, and are partially separated by open seams, and on the 
front of bluffs or ledges the rock has consequently a riband-like 
appearance. ‘The layers often coalesce and subdivide without regu- 
larity, though uniformly parallel. They are frequently twisted, and 
thus change, at short intervals, from a vertical position to a dip of 
twenty degrees. The colours, red and yellow, are often mingled, and 
sometimes appear as parallel bands. In some instances the surface 
is red, while the rock is yellow beneath: this has resulted from the 
burning of a tree on the spot; for by heat the yellow variety readily 
changes to red. A small specimen of the green variety had an agate- 
like structure, as if it had been formed from an aqueous solution. 
The rocks which have been described illustrate metamorphic action 
in an interesting manner; but we content ourselves here with simply 
stating the facts. The term Plutonic has been here used for conve- 
nience in an extended sense. 
Decomposition.—The granitic regions of South Oregon are mostly 
covered with a dry gravelly soil or fine sand, from the granulation of 
the material instead of its decomposition. ‘The sterile sands near the 
Shasty River, and over the country for fifteen miles north of the 
Boundary Range, arise from the disintegrated granitic rocks. The 
contrast of granitic and basaltic soil was strikingly displayed in the 
latter region: we passed abruptly from the unproductive sands of the 
feldspathic granite to a mellow loam arising from a basaltic dike. 
The dike was half a mile wide; and or leaving it, the transition was 
as abrupt again to granite sands. 
The compact hornblende and talcose rocks undergo slow change, 
and give a rough, bristly appearance to the country, owing to the 
many projecting points of ragged rock. ‘The plains in the vicinity of 
these rocks are strewed with pebbles they have afforded, among which 
there is a large proportion of milky quartz from the veins or seams. 
The soil from these rocks may be at once distinguished by its harsh 
gravelly character, and a pale brick-red colour. The semi-translucent 
prase on exposure becomes opaque-white, showing that, although 
nearly as hard as quartz, there is still some other mineral, — 
feldspar,) in its constitution. “a 
With regard to the mineral productions of the rocks described, we 
have only the negative fact that nothing of interest has yet been dis- 
covered within the limits of Oregon. ‘The talcose and allied rocks of 
the Umpqua and Shasty districts resemble in many parts the gold- 
bearing rocks of other regions: but the gold, if any there be, remains 
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