Historical:Prospect Hill Siltstone
Elwood Atherton, Charles Collinson, and Jerry A. Lineback
The Prospect Hill Siltstone (Moore, 1928, p. 20; Workman and Gillette, 1956, p. 30), named for Prospect Hill, near Burlington, Iowa, was originally designated a member of the Hannibal Formation, but Workman and Gillette (1956) differentiated the uppermost beds as the Starrs Cave Formation and made the Prospect Hill a formation in the North Hill Group.
The abundant conodonts in the Prospect Hill show a close correlation with the upper part of the Chouteau Limestone (Collinson, 1961, 1964).
Extent and Thickness
The Prospect Hill Siltstone occurs in extreme western Illinois within the area underlain by the McCraney Limestone (fig. M-9). It has a maximum thickness of 29 feet but thins eastward to its boundary. It is exposed above the McCraney along Fall Creek in southern Adams County (SE 23, 3S-8W).
The Prospect Hill Siltstone is conformable with the underlying McCraney and the overlying Starrs Cave, but where the latter is absent it is overlain unconformably by the Burlington Limestone.
The siltstone is light gray to buff, calcareous, pyritic, massive, and friable.
The Prospect Hill contains few macrofossils, however, conodonts are abundant.
COLLINSON, CHARLES, 1961, Kinderhookian Series in the Mississippi Valley, in Northeastern Missouri and west-central Illinois: Kansas Geological Society Guidebook, 26th Annual Field Conference, Missouri Geological Survey Report of Investigations 27, p. 100-109; Illinois State Geological Survey Reprint 1961-U.
COLLINSON, CHARLES, 1964, Western Illinois: 28th Annual Tri-State Field Conference, Quincy, Illinois, Illinois State Geological Survey Guidebook Series 6, 30 p.
MOORE, R. C., 1928, Early Mississippian formations in Missouri: Missouri Bureau of Geology and Mines, v. 21, 283 p.
WORKMAN, L. E., and TRACEY GILLETTE, 1956, Subsurface stratigraphy of the Kinderhook Series in Illinois: Illinois State Geological Survey Report of Investigations 189, 46 p.
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