300 THWAITES AND TWENHOFEL THE WINDROW FORMATION 



a better exposure a few rods north of the west end of the bridge at 

 Mitchell (4 miles northwest of Osage). The latter locality was visited 

 by the senior author in 1920. The material is exactly like that at Waukon 

 and in Wisconsin — concretionary brown and yellow limonite, in large 

 part set full of quartz and black and gray chert pebbles. The pebbles 

 have a maximum diameter of three-quarters of an inch. There is also 

 much sand associated with them. The deposit fills an erosion channel in 

 the underlying Devonian limestone. The elevation at both the Mitchell 

 County outcrops is about 1,200 feet. 



McGee (16) describes "a conglomerate of rounded quartz pebbles im- 

 bedded in a matrix of impure limonite" in the northeast ^4=7 section 11, 

 township 100, range 12 west, four miles northeast of Lime Springs, How- 

 ard County. This formation is said to be present on several hilltops. 

 The bedrock is the Devonian limestone and the elevation is about 1,200 

 feet. 



Bain describes sandstones and conglomerates in Guthrie and Carroll 

 counties which rest unconformably on the "Coal Measures." The sand- 

 stones are soft, of yellow and red colors, and much cross-bedded (3, 4, 

 19). In them are a few thin layers of blue and white plastic clay. The 

 conglomerates carry "small, smooth and well rounded pebbles of white 

 and pink quartz and black chert." The chert pebbles contain Silurian 

 and possibly Devonian fossils. A few poorly preserved fossil leaves of 

 Mesozoic aspect have been collected from the sandstones, while fragments 

 of similar sandstones containing Cretaceous fossils have been found in 

 the glacial drift (4). The senior writer visited the Guthrie County ex- 

 posures in 1920. Eoad grading has made many more opportunities to 

 study the deiJosits than were formerly available. The base of the forma- 

 tion is well exposed in section 24, township 80, range 31 west. Just west 

 of the bridge over Eacoon River 6 feet of gravel rests unconformably on 

 about 11 feet of Coal Measures shale. The pebbles are small and consist 

 of white and pink quartz and gray, yellow, and black chert. The matrix 

 is a coarse yellow sand. Parts of the deposit are cemented by brown 

 limonite which is distinct from the occasional iron concretions, which 

 were probably derived from the underlying Carboniferous. Cross-bed- 

 ding dips west. 



A cut on the State road east of Guthrie Center, in section 4, township 



79, range 31 west, shows the following section: 



Feet 

 (4) Sandstone, coarse, yellow, streaked with brown limonite; beds 2 to 3 



inches ; small pebbles on bedding planes 1 



( 3 ) Gravel like that described above 7 



(2) Shale, bluish gray mottled with brown spots 11 



