Bulletin of the Geological Society of America . FiGuuE 2.—SK-et(]t Mau of Portion of Xorth Thompson TrenchShowing location of Eocene sediments and Miocene lavas. 586 W. L. UGLOW PENEPLAIN IN BRITISH COLUMBIA ridges, constituting foothills to the main valley slopes, on either side ofthe river. In all of the exposures the formation strikes parallel to thetrend of that part of the trench in which it lies, but in each case the bedsdip 20 to 25 degrees toward the eastern side of the trench. No completestratigraphic section is exposed from which the thickness of the forma-tion could be determined. T
Bulletin of the Geological Society of America . FiGuuE 2.—SK-et(]t Mau of Portion of Xorth Thompson TrenchShowing location of Eocene sediments and Miocene lavas. 586 W. L. UGLOW PENEPLAIN IN BRITISH COLUMBIA ridges, constituting foothills to the main valley slopes, on either side ofthe river. In all of the exposures the formation strikes parallel to thetrend of that part of the trench in which it lies, but in each case the bedsdip 20 to 25 degrees toward the eastern side of the trench. No completestratigraphic section is exposed from which the thickness of the forma-tion could be determined. The limited evidence which is available,however, points to a thickness of at least 2,000 feet. Andesitic and basaltic lavas of Miocene age occur in the lower portionsof the valley, chiefly below the 2,5 00-foot contour. On Skull Hill, inthe vicinity of Louis Creek, the lavas are found between elevations of. ..-^ Figure 3.—North TJwmpsoii Trench from Skull Hill The view was taken looking south down the trench and shows the side slopes of thepresent valley and portion of upland plateau. 2,000 and 3,000 feet, producing a flat, mesa-like top. The erosion rem-nants of these rocks may be seen as rock-defended terraces along bothsides of the valley, in many places overlying the sediments of the CbuChua formation. The separate flows are nearly horizontal, but locallyshow dips up to 20 degrees. POST-TERTIARY ROCKS These are of three types: (1) the glacial drift and erratics wliichmantle the gently undulating uplands beyond the rim of the trench; (2)the giacio-fluvial and Eecent gravels, sands, and silts are now carved GEOLOGY OF THE TRENCH 567 into a series of flats and terraces clinging to the sides of the main valleyand its tributaries to a height of 1,000 feet above the bottom, and (3)Recent lava flows of small ascertained extent, covering some of the Recentvalley fill in U-shaped glacial tr
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1890
