210 Observations upon the Geology and Paleontology 



ity, and of late by general consent, been referred to the 

 Cliemung group of New York, and the beds of Carbonif- 

 erous limestone overlying them. The earlier geological 

 explorers of the northwest, referred the whole series of 

 strata exposed here to the Carboniferous limestone. It is 

 undeniable that a great proportion of the genera of the 

 lower beds of the series are common to the mountain 

 limestone ; and also that many of the species have a close 

 resemblance to others of that formation, particularly to 

 the upper members of it, closer to these, in fact, than to 

 any which are strictly referable to the Burlington lime- 

 stone, between which and the lower beds a marked con- 

 trast is presented in their fossils when grouped separately. 

 This general resemblance of fossils of known Devonian 

 origin to others found in the Carboniferous rocks, and 

 their gradual dying out and replacement by Carboniferous 

 species, it is at present proposed to notice, together with 

 other matters tending to show that in this locality at least 

 the Carboniferous system was ushered in with the utmost 

 tranquillity ; the final change from Devonian to Carbonifer- 

 ous taking place so gradually as to render it impossible 

 to point out the exact line where one ends and the other 

 begins. 



With the hope at a future time to make some compari- 

 sons between these rocks, and others holding a similar 

 geological position in other localities, this communication 

 will be mostly confined to a consideration of the strata 

 exposed at Burlington, and traced above and below the 

 city for several miles along the precipitous blutTs of the 

 Mississippi River, and also the continuation of the same 

 exposure, a few miles up each, on Skunk and Flint rivers, 

 being an almost continuous exposure for about fifteen 

 miles. It would have been desirable that the results of 

 observations made at other localities of the same geo- 

 logical horizon should have accompanied these, yet it is 



