OCCURRENCES 299 



described by Allen (3) is stated by Professor Steidtmann^ to contain no 

 quartz or chert pebbles, and therefore can not be definitely correlated with 

 this formation. 



IOWA 



The best known occurrence of the Windrow formation in Iowa is near 

 Waukon, Allamakee County, where it caps an elevation of about 1,360 

 feet known as Iron Hill (sections 17 and 20, to^vnship 98, range 5 west). 

 This occurrence has been described by Orr (18), Calvin (6), Beyer (5), 

 and Howell (12) and was visited by the senior author in 1919. The de- 

 posit consists of concretionary, bouldery, hydrous, manganiferous iron 

 oxide covering several hundred acres. It has been carefully explored for 

 iron ore by the Missouri Iron Company and a great deal of development 

 has been done, so that conditions for study are excellent. Parts of the 

 deposit show much sandstone and iron-cemented conglomerate witli 

 quartz and black chert pebbles like those in Wisconsin. The main part 

 of the ore body is fairly free from pebbles and has a maximum thickness 

 of about 135 feet. It is separated from the underlying Galena dolomite 

 by a foot or two of residual red clay. Large dolomite boulders and silici- 

 fied and limonitized fossils occur at some points in the limonite. The 

 minerals present include limonite (the most abundant), turgite, gothite 

 ( ?), wad, various manganese oxides, and hyalite. iVnalyses show the fol- 

 lowing variations in composition (5, 12) : 



Per cent 



Iron 6.77 to 66.92 



Phosphorus .* 0.072 to 1.87 



Manganese . 33 to 1 . 02 



Silica 3.92 to 60.25 



Alumina 3.57 tolS.OS 



Calvin (6) mentions two other deposits in the same county, one (south- 

 east 1/4, section 27, township 98, range 5 west) at an elevation of about 

 1,200 feet and the other (northwest corner section 6, township 97, range 

 4 west) at about 1,100 feet. 



Alden (1) describes a locality "a few miles southeast of Eockford, 

 Floyd County," as "1 foot to 9 feet of soft buff sandstone (in places loose 

 sand) set full of small, rounded, highly polished fossiliferous black chert 

 and white quartz pebbles." This deposit caps low mounds at an elevation 

 of not over 1,100 feet and rests on the Devonian. 



The same author describes "similar sand and gravel . . . al)out 8 

 miles northeast of Osage, Mitchell County'' (southwest 14, section 15, 

 township 99, range ]6 west).. Calvin also mentions this deposit (8) and 



^ Edward Steidtmann : Personal communication. 



