File:Bulletin of the Geological Society of America (1923) (14779505554).jpg

Identifier: bulletinofgeolo341923geol (find matches)
Title: Bulletin of the Geological Society of America
Year: 1890 (1890s)
Authors: Geological Society of America
Subjects: Geology
Publisher: (New York : The Society)
Contributing Library: Smithsonian Institution Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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Paleozoic. The age of the intrusive rocks has not beendefinitely determined. Some of them may be of Precambrian age, someof them are believed to be Jurassic, and others may even be Tertiary. The attitudes of the foliated or bedded rocks are not parallel to themain northwesterly Cordilleran trend. They strike east, northeast, ornorthwest with very little tendency to exhibit any regularity. TERTIARY ROCKS These are of two ages—Middle or Upper Eocene and Miocene. The Eocene, or Chu Chua formation, consists of a series of basal con-glomerate (or agglomerate), highly feldspathic arkose, sandy shale, andsub-bituminous coal. These rocks occur in the bottom and along thelower slopes of the Xorth Thompson trench, in isolated erosion remnants,the highest exposures found being at an elevation of about TOO feet abovethe level of the river (see figure 4). They underlie a few narrow low For full discussion see Summary Rept. Geol. Siirv. Canada, part A, 1921, pp. 72-106. GEOLOGY OF THE TRENCH 565
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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

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