NIAGARA LIMESTONE. 353 



Fossils OF THE Uppek Cokal Beds of the Niagaba GnovF — 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 iind the central, and, to 

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

 pied by the Coral beds, tlie 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 m vertical cliffs, facing the lake. The exposure belongs chiefly to the 

 upper division, and presents, in certain poi-tions, more than the usual amount of cherty 

 material. In general, the beds are highly fossHiferous. Silicified specimens of PenU- 

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



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

 Wis. SuR. —23 



