244 ILLINOIS STATE ACADEMY OF SCIENCE 



horizon. In some places in northern Illinois and north- 

 eastern Iowa the upper, very fossiliferous beds of the 

 Maquoketa "were removed by erosion before the overly- 

 ing Silurian strata were deposited. In other places a 

 thickness of 25 to 50 feet of non-fossiliferous shale over- 

 lies this calcareous, and very fossiliferous horizon. The 

 latter can be traced clearly from northern Illinois across 

 the northeast part of Iowa, in spite of the erosional un- 

 conformity at the top which results in different levels 

 of the Maquoketa occurring immediately beneath the Sil- 

 urian limestone. 



An excellent outcrop of these upper Maquoketa strata 

 occurs along a stream 7 miles west of Preston, in Jack- 

 son County, Iowa, where the following section was made : 



SECTION OF STRATA EXPOSED 7 MILES WEST OF PRESTON, IA. 



Ft. 

 Silurian limestone 



Limestone, dolomitized, in rather even layers 4 to 12 inches 



thick, containing few fossils , .. 40 



Maquoketa shale 



Shale, bluish-gray, in thin layers. Those in the upper part 

 alternating with limestone bands, containing many fossils... 35 



The following species were collected from the Maquo- 

 keta shale at this locality : 



FOSSILS FROM THE UPPER PART OF THE MAQUOKETA, 

 7 MILES WEST OF PRESTON, IA. 



1. Anolotichia sp. (r-c) 



2. Anaphragma mirabile ? (c) 



3. Batostoma sp. (c) 



4. Bythopora meeki (James) (r) W. L. Wh. 



5. Ceramoporella ohioensis (Nich.) (r) Richmond 



6. Coeloclema sp. (r) 



7. Corynotrypa inflata (Hall) (c) Richmond 



8. Eridotrypa simulatrix (r) W. 



9. Hallopora subnodosa (Ulr.) (c) Richmond 



10. Hallopora sp. (c) 



11. Homotrypella rustica ? (r) W. L. Wh. 



12. Mesotrypa sp. (c) 



13. Peronopora decipiens (Rom) (r) A. E. 



14. Petigopora sp. (c) 



15. Stigmatella spinosa (r) W. 



16. Stigmatella sp. (c) 



17. Stomatopora arachnoidea (Hall) (r) 



18. Rhombotrypa quadrata (Rom.) (r) W. L. Wh. 



19. Rhombotrypa subquadrata (Ulr.) (r) W. L. 



20. Streptelasma rusticum Billings (r) W. L. Wh. E. 



21. Dalmanella tersa Sardeson (r) 



22. Dalmanella testudinaria (Dalman) (c) 



23. Dinorthis subquadrata Hall (r) L. Wh. 



