. 108 . IOWA ACADEMY OF SCIENCES. 



the points in a very different light from that in which they 

 were originally presented. Standing now after a lapse 

 of sixty years, one cannot bnt marvel at the wonderful dis- 

 cernment with which the first efforts to differentiate the 

 Carboniferous formations were made. Time has notdimmed 

 the work of that indefatigable pioneer in American geology, 

 David Dale Owen, in his discriminations concerning the 

 Carboniferous limestones of the Mississippi valley. 



The arrangement of the geological formations as proposed 

 by Owen rests primarily upon lithologic grounds; but fossils 

 receive their full consideration. So far as it goes, Owen's 

 scheme is essentially the ])lan now accepted. New titles 

 have been proposed, but the actual divisional lines remain 

 unaltered. To the shales underlying the Encrinital (Bur- 

 lington) limestone at Burlington and Hannibal Owen gave 

 the name Argillo-calcareous group. Although the nether 

 limit was not specific the group is known to be practi- 

 cally co-extensive with what was later termed the Hannibal 

 formation. 



When fresh from the rich paleontologic fields of New 

 York, where a standard Paleozoic section for America had 

 been recently established, James Hall was easily led to 

 discern in the rocks of the Mississippi valley the faunal 

 horizons which he knew so well in his native state. In the 

 Argillo-calcareous group of Burlington and Hannibal he 

 fancied that he recognized the Chemung of the East. He 

 had already traced the Devonian formation westward to the 

 Mississippi river. 



The determination of the Devonian age of the shales at 

 the base of the section at Burlington and at Hannibal did 

 ^not rest upon observations at these points alone. There 

 was a correlation of these beds w^ith lithologically similar 

 beds farther to the northward at Muscatine and in northern 

 Iowa where there was an obvious association with un- 

 doubted Devonian limestones. Singularly enough, after 

 forty years of uncertainty Hall's correlation and assignment 

 of Devonian age to these strata, are again beginning to be 

 demonstrated to be correct. At no time during all the 



