Devonian Rocks Exposed in Vicinity of Rock Island, Ills. 93 



ARTICLE X.— A BRIEF DESCRIPTION OF THE SEC- 

 TION OF DEVONIAN ROCKS EXPOSED IN THE 

 VICINITY OF ROCK ISLAND, ILLS., WITH A 

 STATEMENT OF THE NATURE OF ITS FISH 

 REMAINS. 



By J. A. Udden, Rock Island, Ilxs. 



A continuous section of the Devonian rocks exposed along 

 the Mississippi River, where it crosses the east end of the 

 Iowa area of this system, has not yet been published. I 

 believe that the summary given below will prove to be nearly 

 correct. The description begins with the lowest bed and 

 continues upward. 



1. A very pure limestone, bluish-gray or white, mostly 

 thin-bedded, often brecciated, without fossils, except in the 

 lowermost ledges, where a small Spirifer and a minute coral 

 occur, and in the uppermost layers, where a single specimen 

 of a cyathophylloid coral has been observed. Thickness about 

 70 feet. This limestone was referred to the Upper Helder- 

 berg by James Hall in 1858. The lower fossiliferous part 

 appears to be the same as Prof. W. H. Norton's Otis beds. 

 The greater part of these beds have by the latter author been 

 called the Lower Davenport beds. Others have referred 

 them to the Corniferous. 



2. Three or four ledges of a strong, somewhat granular, 

 thick-bedded limestone, with large cephalopods numerous 

 corals and brachiopods and other fossils. Thickness about 

 7 feet. In part, the Hamilton limestone of Worthen ; the 

 Gyroceras beds of Calvin and Barris; the Upper Davenport 

 beds of W. H. Norton. Referred by Barris to the Corniferous. 



3. Three ledges of a fine-grained, bluish limestone, sep- 

 arated by seams of green shale, and containing brachiopods 

 in profusion. Thickness, 6 feet. Referred by most older 

 writers to the Hamilton age. The lower part of the Cedar 

 Valley limestone of the Iowa geologists. 



(Jour. Cin. Soc. Nat. Hist., Vol. XIX, No. 3.) 1 Printed Nov. 13, 1897. 



