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The AAPG/Datapages Combined Publications Database

Kansas Geological Society


Upper Mississippi Valley, Iowa City, Iowa to Duluth, Minnesota: 9th Annual Field Conference, 1935
Pages 383-385

Cambrian Inlier at Oregon, Illinois

Arthur Bevan


During the survey of the Oregon quadrangle for the Illinois State Geological Survey in 1923-28 the writer discovered that certain outcrops along Rock River east of Oregon, Ogle County, are Cambrian; that the lowest rock exposed is a white sandstone either Galesville or St. Peter in age; that St. Peter sandstone is unconformable upon the Trempealeau and higher beds; and that quartzite breccia along a low strike ridge east of Oregon and erratic dips of Galena dolomite along the strike to the northwest appear to denote a local thrust fault along the northeast flank of the general structure known as the La Salle anticline. This is the first known exposure of Cambrian beds in Illinois and the only positive suggestion of thrust faulting in the northern part of the State.

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