296 THWAITES AND TWENHOFEL THE WINDROW FORMATION 



OCCUERENCES 



WISCONSIN 



The first known occurrence of the Windrow formation in Wisconsin is 

 that near Seneca, Crawford Countj^ (northwest ^4? section 10, township 

 9, range 5 west), where it caps a hill at an elevation of about 1,350 feet. 

 This outcrop was discovered by Strong and later described by Chamberlin 

 and Salisbury (25, 9). Conglomerate of small quartz pebbles in a matrix 

 of sandy manganiferous limonite covers about an acre of ground, while 

 loose gravel is found over a more extended area. An old shaft, now fallen 

 in, is stated by Chamberlin and Salisbury (9) to have shown that the 

 conglomerate extends into a crevice in the Trenton limestone to a depth 

 of 65 feet from the surface. They also state that the average depth of the 

 deposit is from 5 to 6 feet. 



The best known occurrence of the Windrow formation in Wisconsin is 

 on the top of the East Bluff, at Devils Lake (northeast 14, southeast 14? 

 section 24, township 11, range 6 east), where loose gravel is found at an 

 elevation of about 1,440 feet overlying the polished and water-worn sur- 

 face of the Huronian quartzite.- Descriptions of this deposit have been 

 published by Irving, Chamberlin, Salisbury, and Alden (13, 8a, 14, 21, 

 1). Salisbury states that a well disclosed a thickness of 16 feet of gravel 

 at a point back from tlie edge of the bluff, but a pit dug by Alden and 

 Thwaites by the side of the well indicated that the predominant material 

 at that point is deoxidized loess and residuum from Paleozoic limestones 

 and conglomerates. No true gravel was discovered in the excavation. A 

 most striking feature at Devils Lake is the occurrence of several well 

 developed pot-holes in the quartzite. Chert pebbles collected near by 

 show percussion marks similar to those formed in the flint pebbles used 

 in ball mills, and it is suggested that these were made in the formation 

 of the pot-holes. The pot-holes are in no way related to glaciation, as 

 this locality is, beyond reasonable doubt, in the Driftless Area. 



The type locality of the formation here discussed is on Windrow Bluff, 

 an outlier of the Oneota escarpment between Tomah and Sparta, on the 

 divide between Lemonweir and La Crosse rivers (northeast i^, north- 

 west ^, section 10, township 17, range 2 west). This occurrence was 

 discovered by the senior author and Prof. Lawrence Martin in 1916. A 

 small ledge exposes limonite-cemented conglomerate and ferruginous 

 sandstone which rest on the Madison (?) and Jordan sandstones of the 

 uppermost Cambrian. The pebbles are the same as elsewhere, but a few 



~ This elevation is based on splrlt-leveling by engineering stndents and on uarometi'Ic 

 observations by R. D. Irving (14). The U. S. Geological Survey map is incorrect. 



