CAKBONIFEBOTTS SYSTEM. 225 



shown by their abundant remains in different parts of the 

 world, and the rocks of that age in our own State possess 

 a distinguished reputation in this respect, particularly those 

 of the Burlington limestone. With their crinoidal and fish 

 remains, the Burlington and Keokuk limestones will in the 

 future become more famous among geologists, perhaps, than 

 any other formations in North America. Next to those just 

 mentioned, the most conspicuous fossils of the Sub-carbonifer- 

 ous rocks of Iowa are Brachiopods. 



With the exception of a very little carbonaceous shale in 

 the St. Louis limestone, and some traces of fucoids in the 

 same and other strata, no remains of vegetation have yet been 

 discovered among the Sub-carboniferous strata of Iowa. All 

 other organic forms yet found, belong to the animal king- 

 dom, and are all marine. 



6. THE UNCONFORMABILITY OF THE COAL-MEASURES 

 UPON THE OLDER ROCKS, AND OF THE ST. LOUIS 

 LIMESTONE UPON THE OLDER FORMATIONS OF THE 

 SUB-CARBONIFEROUS GROUP. 



It has been shown that quite a number of the formations, 

 which in other parts of the country help to make up the full 

 geological series, are wanting in Iowa ; yet, notwithstanding 

 these deficiencies there is, from the Potsdam sandstone to the 

 Keokuk limestone, inclusive, strict conformability of each one 

 of our Iowa formations upon the next preceding one ; even in 

 those cases where several successive formations are wanting 

 from the full geological series between them. That is, there is 

 no lapping back of any of them over another, but their borders 

 gradually recede from each other to the southwestward. It 

 has been explained also, that the Kinjderhook beds, resting 

 all the way upon the Devonian rocks, can be traced from Des 

 Moines county to Pocahontas county, a distance of more than 

 two hundred miles. Then we find the most northerly exten- 

 sion of the Burlington limestone, falling far short of the most 

 northerly point to which the Kinderhook beds have reached ; 



it having been recognized no farther north than the northern 



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