PALEOZOIC ROCKS FOUND IN DEEP WELLS 533 



which were formerly used for cement. The shale is called "soap- 

 stone," by local well drillers; it caves badly. The maximum 

 known thickness is 168 feet at Milwaukee. 



SILURIAN SYSTEM 

 Cayugan Series 

 General. — The Cayugan series is represented in Wisconsin by 

 the very thin and discontinuous Waubakee dolomite which is 

 found in spots along the Lake Michigan shore. 



NiAGAEAN Series 



CLINTON AND LOCKPORT GROUPS 



Distribution. — The Niagaran series of dolomites (Niagara 

 formation of old reports) forms a conspicuous series of cuestas 

 which extend south from the Door Peninsula in Wisconsin. South 

 of Kewaunee County, Wisconsin, the minor escarpments which 

 mark the different formations are covered by drift and south of 

 Ma3rville, Wisconsin, the western edge of the belt is itself buried so 

 deeply that the mapping of the Niagara area is based wholly on 

 well records. In northwestern Illinois the Niagaran dolomites 

 cap the higher hills, and a few scattered outHers are found in south- 

 western Wisconsin. 



Character. — The Niagaran series of Wisconsin consists from 

 the base up of the Mayville, Byron, Waukesha, Racine, and Guelph 

 formations. The Waukesha of northeastern Wisconsin was called 

 the Lower and Upper Coral beds in older literature. Ulrich 

 places the Mayville in the Clinton group, and inasmuch as the 

 Byron is poor in fossils, it is possible that the line of division might 

 be drawn still higher. Ulrich has found a pre-Clinton dolomite 

 (Burroughs dolomite) beneath the Niagaran in northwestern 

 Illinois whose extent and character are but slightly known. 



The Niagaran series is almost wholly light gray to pure white 

 dolomite; locally pink, red, and less commonly, blue colors are 

 met with in the lower portions. In southeastern Wisconsin and 

 northeastern Illinois layers of blue, pink, and red calcareous shale 

 are found near the base, notably at Milwaukee, Union Grove, and 

 Racine, Wisconsin, and at Area, North Chicago, Maywood, and 

 Elmhurst, Illinois. These basal rocks are probably older than the 



