The Magnesian series, which it is proposed to discuss in this paper, consists of several alternating beds of dolomite, dolomitic shale and sandstone. The series lies between the so-called Potsdam sandstone below and the Saint Peter sandstone above. It occurs in widely distributed localities throughout southern Wisconsin, southeastern Minnesota and northeastern Iowa. Nowhere in the states named has either one of the delimiting formations been found absent, save in eastern Wisconsin, where, at a single locality, Chamberlin found an arch of the billowy lower Magnesian rising into actual contact with the Trenton limestone and thinning out the Saint Peter sandstone to zero.*
A résumé of earlier investigations of the extent and contents of the Magnesian series of Minnesota has already been given by the writers.† To that résumé these notes can be added :
In Wisconsin the geologists of the last geological survey . . .