WALCOTT.J WISCONSIN. 175 



Table of the elementary stratification of the Lowest Protozoic sandstones, 



etc. — Con tinued. 



Feet. 

 ( Fine grit. Place of the Menomonie Trilobite 

 Second Trilobite bed.. \ grit (?). White and yellow sandstone, and 



Obolus layers of Black River 15 



Ferruginous Trilobite grits. Schistose sand- 

 stone, containing fork-tailed Trilobite beds 



First Trilobite bed { and Obolus layers 1 to 8 



h.l I Magnesio-calcareous rock, with Obolus and 



^ fork-tailed Trilobite 3 



Highly fossiliferous schistose, siliceo-calcare- 

 ous layers, interlarainated with argillaceous, 

 marly beds, charged with sulphate of iron ; 

 the former full of Lingulas and Orbiculas 



(Fallsof St. Croix) 50 



Sandstone, with oblique lines of deposition, 

 alternating with pebbly sandstones and 

 coarse grits of the Chippewa and Black and 



{ Wisconsin Rivers near the falls 50 to 100 



Place of the Lake Superior ferruginous and 

 argillaceous sandstones, shales, and con- 

 glomerates 5,000 



The geographic distribution of the formation is shown on the map 

 accompanying the report. 



The local details of the sections in Wisconsin are reported upon by 

 Prof. B. F. Shumard. Much of the information here given was used 

 by Dr. Owen in giving the summary of the divisions referred to Forma- 

 tion No. 1, or the lower sandstone. 1 



The sandstones of the south shore of Lake Superior are described by 

 Mr. J. C. Norwood, and a section given of them as seen at the mouth of 

 Cranberry River. He also describes the sandstones of the St. Croix 

 River. 2 



In his annual report of the geological survey of the State of Wiscon- 

 sin Prof. J. G. Percival describes the lower sandstone with consider- 

 able detail, but without special addition to the information given by 

 Dr. Owen. He separates, however, the quartz rock of the Baraboo 

 and of Portland from the Lower sandstone. 3 



The volume of the geological survey of Wisconsin, by Prof. James 

 Hall, contains a general account of the Potsdam sandstone. The open- 

 ing paragraph describes it as follows: 



The lowest rock of the series is the Potsdam sandstone, which is known in the north- 

 west as the Lower sandstone, in contradistinction to the Upper or St. Peter's sand- 

 stone, which lies above the Lower Magnesian limestone. This is equivalent to the 

 Potsdam sandstone in New York, and holds in all respects the same geological position : 

 it is the lowest fossiliferous rock observed in the geological surveys of New York, 

 where it received its name. 



This rock has been traced, with slight interruptions, westward from Lake Cham- 



1 Geol. Keport of local, detailed observations in the valleys of the Minnesota, Mississippi, and Wiscon- 

 sin Rivers. Report of a geological survey of Wisconsin, Iowa, and Minnesota; and incidentally of 

 a portion of Nebraska Territory. Philadelphia, 1852, pp. 475-531. 



2 Geol. Report of a survey of portions of Wisconsin, and Minnesota. Rep. Geol. Surv. of Wisconsin, 

 Iowa, and Minnesota ; and incidentally of a portion of Nebraska Territory. Philadelphia, 1852, pp. 

 275-277. 



•Annual Report of the Geological Surrey of the State of Wisconsin. Madison, 1866, pp. 82-101. 



