Geological Excursion into Central Wisconsin — Hall. 251 

 [Paper BB,] 



NOTES OF A GEOLOGICAL EXCURSION INTO CENTRAL WISCONSIN. — 



C. W. Hall. 



This excursion was made because the writer was desirous of 

 seeing in the field some of the rocks which had been described by 

 Professor Irving and C. R. Van Hise in the reports of the Geo- 

 logical Survey of Wisconsin, and of comparing them with 

 certain Minnesota rocks which he then had under examination. 

 The localities visited were the Wisconsin river valley from Rhine- 

 lander to Stevens Point; the neighborhood of Waupaca, where are 

 situated some notable granite quarries; and the iron ore deposits 

 of Black River Falls. In the few days at his disposal only a hur- 

 ried reconnaissance could be made, but the specimens collected 

 have been subsequently examined more in detail. 



THE WISCONSIN RIVER VALLEY. 



' From Stevens Point, where the Wisconsin Central railroad 

 crosses the river, to its head waters the Wisconsin river is used 

 largely for lumbering operations. One of the richest pineries in 

 the Northwest lies around these upper waters, and a thriving lum- 

 bering industry has grown up along the stream. In area the dis- 

 trict embraces several thousand square miles. Originally it was 

 throughout a timber- covered area, and it is still largely so covered. 

 A thick mantle of glacial debris is well-nigh universal; there are 

 but few rock exposures in the valley, save along the streams, where 

 water has bared and eroded the underlying rocks. 



The Wisconsin river rises near the boundary of the state of 

 Michigan, at 1,530 or more feet above the sea. Until Township 

 23, Range 6, is reached, the stream flows over a bed of glacial 

 drift, save where this has been cut through and the old crystalline 

 rocks are laid bare. In the neighborhood of Stevens Point out- 

 liers of a light-colored to white sandstone are seen, and these soon 

 become a continuous rock formation towards the south, and, a 

 short distance below Port Edward, the crystalline rocks disappear 

 altogether beneath it. This sandstone belongs, according to the 

 Wisconsin geologists, to the Potsdam age, and is undoutedly of the 

 same age as the sandstones of identically the same physical and 

 lithologic characters occurring around Hinckley, Sandstone and 

 along the Snake river in central and eastern Minnesota. In Min- 



