142 IOWA ACADEMY OF SCIENCE 



A NEW STRATIGRAPHIC HORIZON IN THE CAMBRIAN 

 SYSTEM OF WISCONSIN. 



W. D. SHIPTON. 



During the summer of 1915 it was the privilege of the writer 

 \o work on the geology of the Sparta quadrangle, "Wisconsin. 

 In connection with that work a new stratigraphic horizon in thd 

 Cambrian was recognized. 



The normal section of the Cambrian in Wisconsin 1 is as fol- 

 lows: 



Thickness in Feet 

 3. Madison sandstone 35- 50 



2. Mendota limestone 30- 45 



1. Potsdam Proper sandstone 800-1000 



111 the Sparta quadrangle, the Mendota member is missing, 

 2nd a new Cambrian member is recognizable. Because of its 

 wide distribution and excelllent exposures around Sparta, this 

 persistent, shaly member has been named by the writer the 

 Sparta member. Its base lies 290 feet and its surface about 90 

 feet below the top of the Cambrian: that is, the member is ap- 

 proximately 200 feet thick and includes the upper 165 feet of 

 the Dresbach member (Potsdam Proper) and the whole of the 

 Mendota member in the normal section for the state. In the 

 Sparta quadrangle the Cambrian is divided into the following 



members : 



Thickness in Feet 



3. Madison sandstone 90 



2. Sparta shale 200 



1. Dresbach sandstone 820-879 



Many exposures of the Sparta beds arc to be found through- 

 out the region. Two type localities are a quarry two miles 

 southeast of Sparta in the southwest corner of section 30, town- 

 ship 17 north, range 3 west, and a quarry one and one-half 

 miles north of Sparta in the center of section 1, township 17 

 north, range 4 west. From the latter quarry good exposures 

 may be seen by visiting' the series of quarries along the upland 

 to the northeast, The beds are well exposed along the road and 



Irving, Roland D., Geology of Wisconsin, Vol. II, p. 4 60. 



