32 DAVENPORT ACADEMY OF NATURAL SCIENCES. 



The subject thus presented suggests the fault of former papers on 

 " Our Local Geology," in referring the lower beds to the Corniferous 

 limestone. It consisted in emphasizing certain conditions as peculiar 

 to the Phragmoceras beds, when, as we have shown by comparison of 

 bed with bed, it is found that conditions equally characteristic distin- 

 guished the other two. Unity is thus reached, not diversity. The 

 very differentiation of these beds as to lithologic and palaeontologic 

 character, instead of separating, binds them together as parts of one 

 Geological formation. In keeping with such relationship is the fact 

 that one-third of the fossils of the Phragmoceras beds pass up into the 

 Spirifer Pennatus beds, suggesting another bond of union. In the list 

 given how few fossils can be recognized as positively characteristic of 

 the Corniferous limestone. 



Further, and establishing the true relationship of these beds to each 

 other, is the significant fact that there are no signs of disturbance be- 

 tween the Phragmoceras and the Spirifer Pennatus beds that would 

 suggest a separation. Despite a single apparent exception, and that at 

 the summit of the Spirifer Pennatus beds, the same continuity of rock 

 deposition is maintained throughout the whole series. 



Efforts have been made from time to time to correlate the whole or 

 parts of the Iowa Devonian limestone with the whole or parts of the 

 New York Devonian, but have not proved entirely satisfactory. The 

 incorporation of the following remarks of McGee into the first volume 

 of the Iowa Geological Survey by Prof. Keyes, then Assistant State 

 Geologist, no doubt voices the opinion of the Chief of the Survey, and 

 its reproduction here may well close the present paper.* 



''It is therefore manifestly unwise to correlate either the limestones 

 alone or the entire series of Devonian strata with any of the New York 

 divisions; and While the shales may be discriminated on both litho- 

 logic and palseontologic grounds, it is not now possible ( and perhaps 

 it never will be possible) to separate the limestone series into distinct 

 formations or into individualized beds of more than local 'alue. They 

 may accordingly be treated as a unit and may take an individual name ; 

 and it seems expedient to recur to the designation originally proposed 

 by Owen, and re-christen the entire series of Calcareous sediments 

 stretching from the Minnesota line to Muscatine County in a belt 

 fifty miles in average width, the Cedar Valley Limesto7ie.'' 



* U. S. Geol. Surv., nth An. Rept., page 319. 

 Iowa Geol. Surv., Vol. I., page 39. 



