3 



Beds of passage ; soft shaly or marly bed, with geodes of 

 quartz, chalcedony, &c. 



II. Keokuk limestone, or Lower Archimedes limestone. 



Localities. — Keokuk, Quincy, 111., etc. 



Beds of passage : Cherty beds 60 to 100 feet. Rapids 

 above Keokuk. 



I. Burlington limestone. 



Localities. — Burlington, Iowa ; Quincy, 111. ; Hannibal, etc., Missouri. 



Oolitic limestone and Argillaceous sandstone of the age 

 of the Chemung group of New York. 



Localities. — Burlington, Iowa ; Hannibal, Missouri. 



The species of fossils here described are from No. Ill of 

 the section. A large number of these occur at Spergen Hill 

 and Bloomington, Indiana; others in the same position and 

 association on the Mississippi river above Alton. I have al- 

 so learned from Prof. Bailey, since these descriptions were 

 written, that Dr. Owen sent to him, some years since, some of 

 the Polythalamia and other minute fossils from Clear Creek, 

 Monroe county, Ind. ;* and I have had in my collection for 

 several years a specimen of the rock from Spergen Hill, con- 

 taining at least ten or twelve of the species now described ; 

 but they had not heretofore attracted my especial attention. 



The bed at Spergen Hill is highly oolitic. The Rotalia 

 are extremely abundant, and likewise the Gasteropoda, most- 

 ly of minute but well characterized species. At Blooming- 

 ton many of the species are of larger size, but the individ- 

 uals are less abundant. On the Mississippi river, above Al- 

 ton, Illinois, some two hundred and fifty miles northwest of 

 Bloomington, the Brachiopods and Lamellibranchiate shells 

 are abundant, while comparatively few species of Gastero- 

 poda occur there, and these not in the same abundance as at 

 Spergen Hill and the other eastern localities. 



The oolitic character of the rock at Spergen Hill, the great 



* Some specimens sent by Dr. Owen from Illinois, are alluded to by Prof. 

 Bailey in a paper on American Polythalamia, in the American Journal of Sci- 

 ence, 1845. 



