I08 ILLINOIS ACADEMY OF SCIENCE. 



rana and Ambocoelia umbonata, occur in the Dakotan province, 

 and both of these are cosmopolitan forms. 



Of the forty-one species listed by Hutton- from Jersey and 

 Calhoun counties, thirty-five, or 87 per cent, are found in the 

 Rock Island county Devonian strata, while only twenty-five, or 16 

 per cent, of the 151 species listed by Savage from the Hamilton 

 strata of Jackson and Union counties of southwestern Illinois are 

 found in the Rock Island county strata, and nearly all of the 151 

 species are of the Eastern province. Therefore the close rela- 

 tionship of the Devonian strata of Jersey and Calhoun counties 

 and those of Rock Island county to those of the Dakotan province 

 is conclusive proof that both belong to this province, of which 

 they constitute the southward and eastward extension ; while the 

 similarity of the fauna of the Hamilton strata of Jackson and 

 Union counties to that of the New York or Eastern province 

 unquestionably proves that they form a part of that province. 

 The land barrier shown as extending across central Illinois in 

 Schuchert's paleogeographic map of late Hamilton time, known 

 as the Kankakee axis, separated the basin in which the deposits 

 of the Eastern province (including Union and Jackson counties 

 in southwestern Illinois) were laid down, from the basin in which 

 the Hamilton strata of Rock Island and Jersey and Calhoun 

 counties were deposited. 



The fauna of the Wisconsin Hamilton is a mixture of the 

 faunas of the Eastern and of the Northwest or Dakotan prov- 

 inces. These forms lived in an arm of the sea in which the waters 

 of the two basins mingled. Only thirty-six, or 37 per cent, of the 

 ninety-seven species found in Rock Island county also occur in 

 Wisconsin, and of these thirty-six species, nineteen, or 52 per 

 cent, occur only in the Dakotan province, while seventeen, or 48 

 per cent, occur in both provinces. 



The Hamilton strata of the Dakotan province in Rock Island 

 county comprise equivalents of the Wapsipinicon and Cedar Val- 

 ley stages of the Hamilton in Iowa. All of those strata below 

 and including the Phillipsastrea bed are the equivalent of the 

 Lower and Upper Davenport divisions of the Wapsipinicon stage 

 of the Iowa strata, the lithological characters (of which breccia- 

 tion is the most conspicuous) and the stratigraphic position of 

 these strata beins: the basis of correlation. The Hamilton strata 



* Hutton, J. G. Thesis for degree of Master of Science in Geology in the Graduate 

 School of the University of Illinois. The stratigraphy of the Devonian rocks of Cal- 

 houn and Jersey counties, Illinois, yKith a preliminary discussion of the physiography 

 of the region. 



