GEOLOGY OF NORTHERN" WISCONSIN". 61 



large Lingulas. Fossils aie also numerous at other localities. At 

 Osceola, six miles from the Falls, trilobite fragments are especially 

 abundant. Among others, I was able to detect the following: 

 ConocephaUfes hlnodosus. C. diadematus, Illaenurus qiiadratus, 

 Agnostus disparilis, and Bikelocephalites osceola. Associated with 

 them is a very large gasteropod, believed to be new to science.. 



Dr. Owen, Avhose observations only have been published upon 

 the geology of the St. Croix, considered the crystalline rocks at the 

 Falls and Dalles of the St. Croix, of igneous origin, and of more 

 recent age than the contiguous sandstones. I submit the following 

 reasons for differing with him upon the question of age: 



1. So far as can be determined, the sandstones are perfectly hori- 

 zontal, and show no signs whatever of ever having been subjected 

 to igneous or metamorphic action, or even of ever having been in 

 contact with highly heated rocks. 



2. Horizontal layers of fossiliferous sandstone occur a few feet 

 from Cupriferous rocks, and in two instances perfect specimens of 

 Oholella polita and Lingideins j^innaeformis were found in a film of 

 sandstone, not over one eighth of an inch from the absolute base 

 of the formation at those points. In other instances shells were 

 obtained from sandstone largely made up from the unaltered grains 

 of the underlying formation. These shells certainly would have 

 been destroyed, thus near highly-heated rocks. 



3. Depressions and pockets in the surface of the Copper-Bear- 

 ing rocks are often found filled or partially filled with horizontal 

 layers of sandstone. 



4. Grains from the crystalline rocks appear in the layers of sand- 

 stone at a distance of several rods from ledges of the former, thus 

 showing that part of their material at least was derived from the 

 Copper-Bearing rocks. The layers of sandstone were deposited 

 therefore after the Cupriferous strata had assumed nearly their 

 present condition. 



Occasional outcrops of the Potsdam occur along the banks of the 

 St. Croix for nearly forty miles above the Falls. A short distance 

 below the mouth of Kettle River, on section 16, town 39, range 19 

 west, the most northern exposures of light colored sandstone were 

 found. The outcrops are in the banks of the stream from ten to 

 forty feet above the surface of the water. They are underlaid by 

 melaphyrs, amygdaloids, conglomerates and fragments of aluminous 



