NO. T3 DIKEr.OCEPIIALUS AND OTHER GENERA 353 



FORMER GENERIC REFERENCE. PRESENT GENERIC REFERENCE. 



Dikelocephalus tasmaiiiciis Etheridge (Proc. 

 Royal Soc. Tasmania for 1882, 1883, p. 155, 

 pi. I, fig. 4) Dikclokel>halina Brogger. 



Dicellocephahis f villcbruni Bergeron (Bull. 

 Soc. geol. de France, 3d ser., Vol. 23, 1895, 

 P- 473, pl- 5, figs. 1,2) Dikclokephalina Brogger. 



Dikellocephalus ivahsatchcnsis Hall and Whit- 

 field (U. S. Geol. Expl. 40th Pari., Vol. 4- 

 1877, p. 241 ) Olenoides Meek. 



STRATIGRAPHTC POSITION OF THE 

 DIKELOCEPHALIN^ 



It has been evident for several years that the various Cambrian 

 formations of the Upper Mississippi Valley, which had been referred 

 first to the Potsdam and then to the St. Croix sandstones, needed 

 careful revision in relation to their stratigraphic position and suc- 

 cession. 



The original classification of Owen (1852) was superseded by the 

 classification of the Minnesota Survey for the Minnesota sections, 

 and for Wisconsin by the classification of the Geological Survey of 

 Wisconsin. The two latter classifications were as follows : 



Wisconsin Minnesota 



1. Madison Sandstone. i. Jordan Sandstone. 



2. Mendota Limestone. 2. St. Lawrence Limestone. 



Calcareous Sandstone. 



Shale. 



Fine quartzose Sandstones. 



Coarse quartzose Sandstone. 



2<A 



Sand and sandy Shales. 



Dresbach Sandstone. 



Shales. 



Hincklev Sandstone. 



During the summer of 19 13 Dr. E. O. Ulrich, who had long been 

 studying the Lower Paleozoic formations of the Mississippi Valley 

 south of Wisconsin and Minnesota, extended his investigations into 

 those states and by combining stratigraphic and paleontologic meth- 

 ods succeeded in delimiting six formations, including the upper 

 Jordan sandstone and the basal sandstone of the Minnesota Survey. 

 He found that the Mendota limestone and the Madison sandstone, 

 which had been previously correlated with the Jordan sandstone and 

 the St. Lawrence limestone respectively of the Minnesota Survey, 

 were both above the Jordan sandstone and separated from it by an 

 unconformity ; also that their included fossils correlated them with 

 the Ozarkian formations of his Missouri section.' 



*Bull. Geol. Soc. America, Vol. 22, 191 1, p. 608, pi. 27. 



