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Igneous Rocks
Outcrops of igneous rocks of undetermined age occur in Riley and Woodson counties. In Riley County there are five known exposures of igneous rocks intruded into sediments of Permian age; in Woodson County granite and fine-grained igneous rocks seemingly are intruded into sedimentary rocks of Pennsylvanian age.
Granite
Coarse-grained granite crops out in Woodson County seemingly in a dike that is partly exposed along a line extending from near the Cen. sec. 13, T. 26 S., R. 16 E. eastward to a point slightly beyond the township line.
Fine-grained Micaceous Rocks
In sec. 32, T. 26 S., R. 15 E., Woodson County, dark fine-grained micaceous rocks that crop out in a small area and occur in the shallow subsurface have been identified as igneous.
Basic Volcanic Rocks
Five outcrops of basic volcanic rocks occur in Riley County. Location of three small outcrops are: sec. 22, T. 8 S., R. 5 E.; sec. 23, T. 8 S., R. 6 E.; and sec. 6, T. 9 S., R. 5 E. Recently two additional occurrences of similar rocks have been found in the northeastern part of the county a few miles north of Randolph.
Metamorphic Rocks
In two localities in Woodson County rocks of Pennsylvanian age have become altered by contact metamorphism.
Quartzite
In southwestern Woodson County in secs. 28, 29, 32, and 33, T. 26. S., R. 15 E., several feet of fine-grained quartzite derived from sandstone in the Douglas group crops out. This rock is associated with fine-grained micaceous rock that has been classed as igneous. Shales and thin limestones in the same area are intensely altered. In sec. 13 some alteration of sedimentary rocks that are associated with outcropping granite has been observed.
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Kansas Geological Survey, Geology
Placed on web Oct. 28, 2008; originally published Jan. 1951.
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