Historical:La Salle Limestone Member
M. E. Hopkins and J. A. Simon
The La Salle Limestone Member of the Bond Formation (Cady, 1908, p. 128-134), the base of which is the base of the formation in northern Illinois, is named for La Salle, La Salle County.
The type section consists of exposures near Bailey's Falls, south of La Salle (14, 33N-1E) (Wanless, 1956, p. 12).
It formerly was correlated with the Millersville and Livingston Limestone Members but is now correlated with the Shoal Creek Limestone.
Extent and Thickness
The La Salle Limestone is well developed in northern Illinois, where it has been quarried extensively (Cady, 1919b). It is as much as 30 feet thick in exposures near La Salle along the west flank of the La Salle Anticline, but it thins westward to about 12 feet west of Spring Valley, Bureau County.
In a belt 1-2 miles wide along its eastern margin, it is a fine-grained, thick-bedded, light gray, nodular limestone containing a few shale partings and a large and diverse marine fauna, mainly brachiopods and gastropods. It grades westward to a fine-grained, argillaceous, tan, brown-weathering limestone that occurs mostly in even beds 4-8 inches thick separated by strong shale partings and containing a restricted marine fauna characterized by large brachiopods, mostly productids.
CADY, G. H., 1908, Cement making materials in the vicinity of La Salle, in Year-Book for 1907: Illinois State Geological Survey Bulletin 8, p.127-134.
CADY, G. H., 1919b, Geology and mineral resources of the Hennepin and La Salle Quadrangles: Illinois State Geological Survey Bulletin 37, 136 p.
WANLESS, H. R., 1956, Classification of the Pennsylvanian rocks of Illinois as of 1956: Illinois State Geological Survey Circular 217, 14 p.
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