Historical:Lonsdale Limestone Member
M. E. Hopkins and J. A. Simon
The Lonsdale Limestone Member of the Modesto Formation (Worthen, 1873, p. 328) is named for the old Lonsdale quarries, Peoria County.
The original type section in the old quarry (N 1/2 6, 8N-7E) is no longer accessible, and an outcrop near by (14, 8N-7E) is a supplementary type section (Wanless, 1957, p. 194).
It is correlative with at least a part of the West Franklin Limestone of southeastern Illinois, the Cooper Creek Limestone of Iowa, and the Madisonville Limestone Member of western Kentucky.
Extent and Thickness
The Lonsdale is a well developed limestone in western and northern Illinois, where it averages 6-8 feet thick and locally is as much as 25 feet thick.
It is a very fine-grained, light gray limestone, conglomeratic in part. Throughout much of its area of occurrence the upper part is nodular.
It contains a large and diversified marine fauna locally rich in fusulinids.
WANLESS, H. R., 1957, Geology and mineral resources of the Beardstown, Glasford, Havana, and Vermont Quadrangles: Illinois State Geological Survey Bulletin 82, 233 p.
WORTHEN, A. H., 1873, Geology and paleontology: Geological Survey of Illinois, v. 5, 619 p.
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