200 ILLINOIS STATE ACADEMY OF SCIENCE 



The Acervularia coral reef is near the middle, above which 

 the layers are mostly limestone or dolomite. The total 

 thickness of the formation is nearly 70 feet. 



The general succession and relations of the Devonian 

 rocks in Rock Island county are shown in the following 

 section : 



Generalized section of the Devonian rocks in the vicinity 

 of Rock Island, Illinois: 



CEDAR VALLEY LIMESTONE. Feet 



10. Dolomite, yellowish-gray to brown, in layers 6 to 24 inches thick, 

 alternating with thinner partings of shale, containing many 

 stromatoporoids and other fossils. Exposed along the creeks 

 both east and west of Andalusia 20 



9. Limestone, thin bedded, gray, with partings of shale, containing 

 many stromatoporoids, Stropheodonta demissa, Schizophoria 

 iowensis, Athyris fultonensis, Atrypa reticularis (large shells), 

 Gomphoceras cf. ajax, and other fossils. Exposed near the mouths 

 of a few streams near Andalusia 4 



8. Dolomite, yellowish-gray, in layers 12 inches or less, containing 

 Cystodictya hamiltonesis, Athyris fultonensis, Spirifer asper, 

 S. subvaricosus, Cyrtina hamiltonensis, small shells of Atrypa 

 reticularis and other fossils 6 



7. Limestone, the upper 1^ feet the Acervularia davidsoni coral 

 reef. The lower part is an organic breccia which in places pro- 

 jects by intersecting vertical plates into the underlying layer. 

 Exposed in the bank of the river below Andalusia, and in the 

 bank of Mill Creek near the center of Section 25, T. 17 N. 

 R. 2 W ••••. 8 



6. Limestone, impure, bluish-gray, crinoidal, thin bedded, con- 

 taining Cladopora iowensis, Megistocrinus latus, Chonetes scitu- 

 lus, Leptostrophia perplana, Spirifer asper, S. iowensis, S. sub- 

 varicosus, Cyrtina umbonata, and other fossils. Exposed at the 

 most of the localities where the overlying coral reef outcrops 5 



5. Limestone, blue, argillaceous, fine grained, with very oblique and 

 prominent jointing. Containing Spirifer iowensis, S. subvaricosus, 

 Cyrtina umbonata, Atrypa aspera var. hystrix, and other fossils. 

 Exposed along Mill Creek; and in the quarries near Linwood 

 and Buffalo, in Iowa • " 20 



4. Limestone, fine-grained, rather thin bedded, with shaly partings, 

 containing Acervularia profunda, Favosites alpenensis, Schizo- 

 phoria iowensis, Pentamerella dubia, Productella subalata, 

 Spirifer asper, S. bimesialis, £md S. iowensis. Exposed in the 

 quarries and ledges in Rock Island, Sears and Milan 5 



WAPSIPINICON LIMESTONE. 

 Upper Davenport Bedsl. 



3. Limestone, hard, gray, in imperfect layers 6 to 24 inches thick, 

 containing Astraeospongia hamiltonensis, Chonophyllum cf. 

 magnificum, Diplophyllun major, Phillipsastrea bilHngsi, 

 Spirifer subundiferous, and other fossils, exposed near the rail- 

 road bridge across Mill Creek, and near the wagon bridges across 

 Rock River. This is the horizon formerly worked in the old 

 quarries in Milan and Rock Island 8 



