T. K. Savage — Stratigraphy of Southwestern Illinois. 439 



uata, Spirifer fornaeula, Conocardium cuneus and Onycho- 

 dus sigmoides. 



The middle portion of the Hamilton limestone is dark 

 colored and evenly bedded, and contains Ambocwlia umbonata, 

 Chonetes yandellanus, C. pusillus, Crancena romingeri, Para- 

 zyga hirsuta, Pholidops oblata, and Spirifer pennatus. 

 Above this horizon occurs about 25 feet of yellowish-brown, 

 impure siliceous limestone with few fossils. Near the top of 

 the formation come in a few feet of hard, gray limestone con- 

 taining Chonetes coronatus, Rhipidomella vanuxemi, Spirifer 

 audaeulus, S. pennatus, Tropidoleptus carinatus and Yitu- 

 lina pustulosa. 



Upper Devonian. — During Upper Devonian time the 

 Mississippian sea continued to expand, spreading the materials 

 of this formation more widely than the preceding. In the 

 JSr.E. \ of section 34, T. 11 S., K. 2 W., the lower deposits of 

 the Upper Devonian are conformable upon the Hamilton. 

 There is here exposed a thickness of 33 feet of yellowish- 

 brown (black where unweathered), siliceous shale or shaly 

 limestone, cherty near the top, and marked by Leiorhynchus 

 globuliformis, L. mesacostalis, Reticularia Icevis and Spiri- 

 fer pennatus. At other points the upper cherty phase is suc- 

 ceeded by 50 or more feet of greenish to black, almost barren 

 shales. These siliceous and dark colored shales are probably 

 the equivalent of the " calico rock," a mottled and leached, 

 siliceous shale, present further south in Union and Alexander 

 counties. They doubtless correspond with the Chattanooga 

 Black Shale, Ohio Black Shale, ]STew Albany Black Shale, 

 and the Lower Portage beds of other states. 



Conclusion. — The present studies have shown that the pre- 

 Mississippian beds have a much wider distribution in south- 

 western Illinois than was formerly supposed. They have dis- 

 tinguished the presence of a bed of blue, fossiliferous shale 

 (2b of section) containing the Cyclocystoides and Phylloporina 

 fauna, immediately overlying the Thebes sandstone and shale 

 horizon. They have demonstrated the presence, in this region, 

 of Silurian beds corresponding with the Clinton formation in 

 Ohio. They have shown that the massive crystalline lime- 

 stone underlying the Clear Creek cherts, in Jackson and Union 

 counties, belongs to the New Scotland formation of the Hel- 

 derbergian. They have demonstrated the Upper Oriskan} T 

 age of the Clear Creek cherts. They have disclosed the 

 absence of the greater portion of the Onondaga formation in 

 the southern portion of Union and in Alexander county ; and 

 they have shown that the Hamilton formation, in Union 

 county, continues upward without a break into the Lower 

 Portage beds of the Upper Devonian. 



The general relations of the formations discussed above 

 may be shown in a composite section as follows : 



