546 F. T. THWAITES 



Devils Lake Formation 



Distribution. — The Devils Lake formation is known only in a 

 few exposures near the quartzite ranges at Baraboo, Wisconsin. 

 It has never been located in a complete normal section away from 

 the old beaches; indeed it is not positively known if all of the 

 supposed occurrences are of the same age. 



■ Character. — The Devils Lake formation consists of gray and 

 yellow, more or less glauconitic sandstone and of quartzite pebble 

 conglomerate. In the best known exposures, southwest of Baraboo, 

 it is underlain by glauconitic sandstone and purple spotted dolomite 

 unlike anything known in the normal section outside the quartzite 

 ranges ; at other places the formation has been found resting on the 

 Jordan, and possibly on other formations. It is overlain in some 

 places by the Mendota dolomite, and in others apparently by the 

 Oneota dolomite. The formation in question is of no importance in 

 the study of well records on account of its limited distribution; it 

 is barely possible that some of the strata in southeastern Wisconsin 

 here ascribed to the Mazomanie formation are Devils Lake. The 

 thickness of the Devils Lake is not definitely known but may reach 

 a maximum of over loo feet. 



CAMBRIAN SYSTEM^ 



Upper Cambrian Series (St. Croix Group) 

 jordan eormation 



Distribution. — The Jordan sandstone outcrops in a narrow 

 belt along the Lower Magnesian escarpment and in the sides of 

 valleys within the cuesta as far east as near Cross Plains, Wisconsin; 

 east of that point it has not been definitely distinguished. On the 

 Mississippi it passes beneath the surface near Prairie du Chien, 

 Wisconsin. 



Character. — The Jordan sandstone is noted for its pure white 

 color although in places some outcrops are yellow. The grain is 

 fine to medium; calcite or dolomite concretions are abundant at 

 the surface. Followed down the dip into northwestern Illinois the 

 formation loses its identity as a lithologic unit and grades into 

 sandy dolomite; no Jordan sandstone has been distinguished in 



' As defined by Ulrich. 



