NIAGARA LIMESTOXE. 



353 



FOSSILS OP THE UPPER CORAL BEDS OF THE NIAG_*RA GROLT continued. 



The greatest thickness of this formation actually observed is 75 

 feet. Its maximum thickness is estimated at 90 feet. 



Distribution. Beginning at the north, we find the central, and, to 

 a great extent, the eastern portion of the Green Bay peninsula occu- 

 pied by the Coral beds, the lower division, of course, lying to the 

 westward. Extending southward, they constitute an irregular belt, 

 occupying a median position on the Lake Michigan slope, and ceasing 

 to be traceable as distinct subdivisions in the southern portion of 

 Fond du Lac county. 



Local Details. Near the eastern entrance of Porte de Morts, the coral beds pre- 

 sent themselves in vertical cliffs, facing the lake. The exposure belongs chiefly to the 

 upper division, and presents, in certain portions, more than the usual amount of cherty 

 material. In general, the beds are highly fossiliferous. Silicified specimens of Penta- 

 merus oblonyus, of rare beauty, are occasionally met with. 



At Bailey's Harbor, the Upper Coral beds are exposed in nearly their entire thick- 

 Wis. SUH. 23 



