PAPERS ON GEOGRAPHY AND GEOLOGY 233 



THE CORRELATION OF THE MAQTJOKETA AXD 

 RICHMOND ROCKS OF IOWA AXD ILLINOIS 



T. E. Savage. University of Illinois 



The rocks of Richmond age in southeastern Iowa have 

 been called the Maqnoketa formation, or Maquoketa 

 shale, from the Little Maqnoketa River in Dubuque 

 County, Iowa, along which they are well exposed. Cor- 

 responding strata also outcrop in the northwest part of 

 Illinois. 



The lower strata of Richmond age in southern and 

 eastern Illinois have been correlated with the Femvale 1 

 limestone. They are exposed in a number of places along 

 the Mississippi River in the southwest part of the State, 

 for example, near Thebes in Alexander County, and near 

 Val Meyer in Monroe County. Outcrops of this lime- 

 stone also occur in adjacent portions of Missouri, as at 

 ■ Girardeau. Strata of corresponding age also out- 

 crop in Will and Kendall counties, in the northeast part 

 of the State. One of the localities in which they furnish 

 an unusual number of bryozoa and other fossils in an 

 excellent state of preservation is in the banks of Kanka- 

 kee River at "Wilmington, Illinois, where the exposed sec- 

 tion is as follows : 



SECTION OF RICHMOND STRATA IN THE VICINITY OF 

 WILMINGTON 



2. Shale, bluish-gray, with few fossils 35 ft. 



1. Limestone, shaly to subcrystalline, in irregular layers that 



contain numerous fossils . . - 12 ft 



The Richmond sediments were deposited on an eroded 

 surface so that in some places in northeastern Illinois a 

 thickness of 40 or 50 feet or more of shale of Richmond 

 age underlies the limestone member exposed at Wilming- 

 ton, This limestone is also in places thicker than in the 

 Wilmington section. There are no fossils in the shale 

 beneath the limestone by which its age can be deter- 

 mined. However, as the two members do not appear to 

 be separated by an unconformity, the shale probably rep- 

 resents the initial deposits of the formation to which the 

 limestone belongs. 



1 Savage. T. E., The faunal succession and the correlation of the pre- 

 r.rions of southern Illinois. Bull. No. 16, 111. State Geol. 

 Survey, pp. 315-31S, 1910. 



