PAPERS OF GENERAL INTEREST 23 



tiated near the middle of the last century, and the foraia- 

 tions defined by James Hall, with some few modifications 

 and additions, are recognized to this day. In this Series the 

 formations now generally recognized are as follows, begin- 

 ning with the uppermost one. 



7. Ste. Genevieve limestone. 



6. St. Louis limestone. 



5. Spergen or Salem limestone. 



4. Warsaw limestone and shale. 



3. Keokuk limestone. 



2. Burlington limestone. 



1. Kinderhook Group. 



The oldest unit in this series, the Kinderhook Group, is 

 really made up of numerous local formations, including 

 sandstones, shales, and limestones. Throughout southern 

 Illinois and adjacent regions, where outcrops of these beds 

 are known, they eveiywhere exhibit a relation of uncon- 

 formity with the underlying strata, a relation which shows 

 that the whole area has been a dry land surface immediately 

 preceding Mississippian time. This condition accounts for 

 the notable heterogeneity of the Kinderhook beds. The per- 

 iod was one of sea advancement during which the basin was 

 bordered by lands from which various sorts of clastic ma- 

 terials were being transported into the sea, in one place 

 mud to form shale, in another place sand to form sandstone, 

 and elsewhere in some sheltered situation where land det- 

 ritus could not reach, limestone beds were accumulated. 

 With the progressive advancement of the shore lines and the 

 gradual submergence of the bordering land area?, the 

 sources of clastic materials were gradually eliminated, and 

 the sedimentary deposits became limestone derived from the 

 skeletons of lime secreting organisms. 



In Burlington time, while the limestone of that name was 

 being accumulated, the submergence had proceeded so far, 

 as is shown by the distribution of the characteristic fossils 

 of Burlington age, that Ozarkia to the west of the basin was 

 largely or wholly under water, and the shore line at the head 

 of the embayment lay somewhere north of the present site 

 of Chicago. The waters connected with this basin spread 



