2 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 326 



The purpose of this report is to describe the bryozoan fauna collected from 

 ten exposures in northwestern Illinois, southwestern Wisconsin, and northeastern 

 Iowa. Discussion of the physical stratigraphy of the Spechts Ferry and detailed 

 consideration of changes in its stratigraphic placement within the Middle Ordo- 

 vician lie outside the scope of this report. The more significant papers dealing 

 with the stratigraphic aspects of the Spechts Ferry are by Kay (1929, p. 639-671; 

 1931, p. 361-376; 1934, p. 328-331; 1935, p. 281-295; 1940, p. 235), Kay and 

 Atwater (1935, p. 98-111), Bays and Raasch (1935, p. 296-301), Templeton and 

 Willman (1952), and Agnew et al . (1956, p. 286-289). 



Lithology of Spechts Ferry Shale 



In the collecting area of this report, dark green, medium gray, and green- 

 gray thin-bedded soft shale is the dominant lithology in the Spechts Ferry Shale. 

 Locally the shale is pyritic. Some Spechts Ferry exposures have a massive or 

 blocky appearance as the bedding is not readily discernible. Bryozoans and other 

 fossils generally are moderately abundant in the shale, particularly if it is some- 

 what calcareous or includes thin beds of highly argillaceous limestone. In con- 

 trast, shale in some excellent Spechts Ferry exposures, such as one located high 

 in a ravine in the SWj NW{ sec. 10, T. 2 N., R. 3 W., near Potosi Station, Grant 

 County, Wisconsin, virtually lacks bryozoans and other fossils. 



Light to medium gray, fine- to medium-grained argillaceous limestone is 

 common in the Spechts Ferry, usually in beds less than 6 inches thick. Fresh 

 surfaces of such limestone beds commonly have a green tint and commonly show 

 discontinuous lenses of soft, dark gray shale that generally are less than 0.5 inch 

 thick and 2 or 3 feet long. Fossils, particularly bryozoans and brachiopods, gen- 

 erally abound on the upper surfaces of limestone beds and in shale immediately 

 above the limestone strata. 



Material Studied 



Bryozoans on which this report is based have been collected from the fol- 

 lowing localities: 



1. Abandoned quarry and ravine, SE^NW^sec. 4, T. 90 N., R. 2E., 



near Spechts Ferry Station, Dubuque County, Iowa. 



2. Abandoned quarry, SW£ NW| sec. 3, T. 90 N., R. 2E., approximately 



1.2 miles southeast of Spechts Ferry Station and about 200 feet south 

 of the C. M. and St. P. rail line, in Dubuque County, Iowa. 



3. Roadcut, SW^sec. 5, T. 92 N., R. 2W., onU. S. Hwy. 52, approxi- 



mately 1 mile north of Guttenberg, Clayton County, Iowa. 



4. Roadcut, NW± SE£ sec. 11, T. 2 N., R. 2 W., 0.25 mile south of the 



intersection of U . S. Hwy. 151 and Blockhouse Creek, Grant County, 

 Wisconsin. 



5. Roadcut, SE£ NW£ sec. 7, T. 2 N., R. 2 W., on U. S. Hwy. 61, 



Grant County, Wisconsin. 



6. Abandoned quarry, approximately 400 feet north of Wis. Hwy. 35, 3.1 



miles east of the junction of Wis. Hwy. 35 and County Hwy. U, Grant 

 County, Wisconsin. 



7. Abandoned quarry, north roadside of Wis. Hwy. 35, 2.6 miles east of 



junction of Wis. Hwy. 35 and County Hwy. U, Grant County, Wiscon- 

 sin. 



