344 GEOLOGY OF EASTERN WISCONSIN. 



About two miles south of the village of Mayville, there is a precipitous cliff 100 feet 

 in hight, exhibiting the full extent, and more than the usual thickness of this subdivision 

 of the Niagara group. Owing to the difficulties of measuring on the vertical face of the 

 cliff, the thickness of the beds is only approximately given from aneroid measurement. 



At the base, are 5 feet of the usual thin bedded, shelly, light colored layers, disinte- 

 grated back from the face of the ledge. 



Overhanging this, is 12 feet of hard, semi-translucent dolomite, not separated into dis- 

 tinct beds, but rifted with vertical fissures, which do not, however, extend into the beds 

 above or below. This supports 7 feet of shaly and cherty rock, lying beneath 4 feet of 

 thick bedded limestone, which is in turn overlaid by 23 feet of shaly and cherty layers, 

 the three forming the shaly or chipstone group, previously described. 



Upon this, lies another stratum of about 23 feet, in which the vertical fissures are much 

 more pronounced than the bedding lines. 



This is surmounted by a somewhat thicker group of soft, white, granular, crystalline 

 dolomite, some layers of which contain many casts of fossils, particularly of Gypiduhi. 

 The top of the ledge is formed of white, fine-grained, crystalline dolomite, closely re- 

 sembling the rock of the next group above, to which it probably belongs. 



In crossing the east branch of Eock river, the boundary again swings to the eastward 

 as in the case of the Rubicon, and in the course of this detour, manifests itself in several 

 low ledges. 



Returning from this deviation, the formation enters upon a succession of precipitous 

 ledges that extend to Little Sturgeon Bay. These are all so like each other, and so sim- 

 ilar to those already described, that it will not be necessary to repeat the details of their 

 structure. From near the village of Kekoskee, the ledges succeed each other in stair- 

 like order, shifting westward till the margin of Horicon Marsh is reached, when they 

 stretch northerly to its extremity, where, forming a continuous rampart, the line curves 

 rapidly to the eastward through the corner of Oakfield, and onward hi crenate outline 

 through the town of Byron. 



The direction of the ledge is now in the line of dip, and the beds under consideration 

 rapidly drop down and are soon surmounted by the white walls of the Byron beds. 

 Turning abruptly northward, in the northwest corner of the town of Eden, the chain of 

 ledges extends through the western part of Empire, the Mayville beds again emerging 

 and forming the rocky rampart, while the white Byron beds retire to the eastward. 

 Opposite the southern extremity of Lake Winnebago, the crown of the cliff, at some 

 points, is formed by a very pure, granular crystalline, cream colored dolomite, locally 

 known as a sandstone. The constituent grains are small crystals of the carbonate of lime 

 and magnesia, usually quite firmly compacted, but sometimes loosely aggregated, leav- 

 ing numerous interspaces, which render the rock very porous and disposed to crumble 

 to a calcareous sand, whence the local name. It is probably due to the misapprehension 

 of its real character, growing out of the use of the name sandstone, that it has not been 

 more extensively used for the manufacture of lime, instead of the much inferior rock 

 that has been employed. Aside from this important stratum, the formation continues 

 essentially as previously described. The chain of cliffs skirts at a little distance the east 

 shore of Lake Winnebago, rising more than 200 feet above it. Toward the northern 

 extremity, the ledge approaches the lake and directly overlooks it. 



Between Lake Winnebago and Green Bay, the formation is more broken down and 

 covered, but on reaching the eastern shore of the latter, it reappears in bold relief, crown- 

 ing and protecting the more perishable Cincinnati shales, and giving a picturesque 

 outline to the bay shore as far north as Little Sturgeon Bay. It forms the rocky sum- 

 mit of Whitney's Bluff, where it is wrought for various purposes. The most northern 

 place where it is extensively used is on the shore west of Little Sturgeon Bay, where 

 a piei and kilns have been constructed. At this point, many of the general features 



