360 GEOLOGY OF EASTERN WISCONSIN. 



graphical position beneath the Racine strata, but nowhere in the 

 southern counties is there manifested that abundance and variety of 

 coralline forms that distinguish the formation to the northward. 

 The Pentamerus beds at Pewaukee bear a closer alliance to certain 

 members of the Lower Coral beds than to any other member of the 

 northern Niagara series, while the white, compact, chertless beds bear 

 so striking a lithological resemblance to the Byron beds, that they 

 have been sometimes regarded as equivalents. But to satisfy all these 

 affinities would be to impose incredible, if not impossiblej demands up- 

 on the stratigraphical relations of the southern members, besides, the 

 affinities are not by any means unequivocal. 



The facts seern to be that in this case, as with the lower formations, 

 the deposits in the southern counties differ from the corresponding 

 ones in the northern counties, and that the Waukesha group of strata 

 is the equivalent of the three more ponderous northern members that 

 lie, like it, between the Mayville and Racine horizons. 



On Plate X of the accompanying atlas, white lines have been used 

 to designate, in a general way, the surface area of each of the sub- 

 divisions of the Niagara group. Within the spaces included be- 

 tween these lines are often limited and occasionally considerable 

 areas of a higher member occupying the summit of prominences, or. 

 of a lower member, reached by deep erosion. Within the general 

 area of the Waukesha beds, patches of Racine limestone occur, as al- 

 ready cited in Genesee. The white lines for this subdivision were 

 drawn so as to include all of the known cherty flags belonging to this 

 horizon. 



KACINE BEDS. 



Overlying the Waukesha beds at the south, and the Upper Coral 

 beds at the north, is a magnesian limestone to which the term Racine 

 has been applied, from its important development at that point. 1 It 

 has an extent of about 200 miles, reaching from Illinois to near the 

 extremity of the Green Bay peninsula, and attains a surface width of 

 thirty miles. In its southern portion, where it rests upon the Wau- 

 kesha limestone, it consists of reef-like masses of conglomeritic rock, 

 which, on the denuded surface, appear as mounds or ridges, and which 

 graduate into various kinds of porous, granular, irregularly bedded 

 rock, or into fine grained, compact, even-bedded strata, the whole con- 

 stituting a formation of exceedingly irregular structure. In its 

 northern portion, where it reposes on the Upper Coral beds, it pos- 

 sesses a much more uniform character. On account of these pecu- 



1 Report of 1862, p. 67. 



