Dale Dome

Location

Southeastern Hamilton County (I-7)

References

Cady et al. 1939, Rolley 1951

Description

Mapping of the Herrin Coal Member (Pennsylvanian) indicates a north-trending dome about 4 miles long by 2 miles wide (6.5 x 3 km); it has at least 50 feet (15 m) of closure (Cady et al. 1939). A structure map of the Beech Creek ("Barlow") Limestone (ISGS open files) shows a dome with about the same amount of closure but smaller areal extent. A test hole drilled on the dome in 1965 reached Precambrian granite at a depth of almost 13,000 feet (4,000 m). The Eau Claire Formation rested directly on granite in this well; the Mt. Simon Sandstone is absent. Such a relationship is common on the buried Precambrian Hills that occur on the Ozark Dome and in the Illinois Basin, and it suggests that Dale Dome is the result of differential compaction around a granite knob.
See also PRECAMBRIAN HILLS.