H. B. Willman and T. C. Buschbach
The Stewartville Member of the Wise Lake Formation (Ulrich, 1911, pl. 27), the upper member (originally the Stewartville Formation), is named for Stewartville, Olmstead County, Minnesota, which is half a mile east of the type section.
The type section of the Stewartville Member is located half a mile west of Stewartville, Olmstead County, Minnesota, in a quarry on the north side of the Root River, where 28 feet of dolomite in the lower part of the member is exposed (Kay, 1935a, p. 567).
Extent and Thickness
The Stewartville Member is about 60 feet thick in the type locality, but only 30-35 feet thick in northern Illinois.
The Stewartville Member is largely thick-bedded, pure dolomite, and many samples from the lower 10-15 feet (the Upper Receptaculites Zone) contain almost no insoluble residue. The bedding becomes thinner upward as a gradual transition to the shaly Dubuque Formation above takes place. The top of the Stewartville is placed at the lowest definitely argillaceous or shaly bedding plane. Above this position is the first occurrence of Pseudolingula iowensis, which is common in the higher, more shaly part of the Dubuque Formation. The Stewartville Member is the Maclurea bed of early reports.
KAY, MARSHALL, 1935a, Ordovician Stewartville-Dubuque problems: Journal of Geology, v. 43, p. 541-590.
ULRICH, E. O., 1911, Revision of the Paleozoic systems: Geological Society of America Bulletin, v. 22, p. 281-680.
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